A broader discussion about skimmers / Tunze DOC 9430 - best skimmer money can buy? / Impact on phosphates?

[Alexander1312]

- Just learned that this skimmer is not available outside the EU as of today (Oct 11, 2025). Also, due to larger footprint, it does require a rather large sump. They seem to be working on a smaller model -

Has anyone tried this one yet?

I believe someone here claimed that skimmer cannot reduce phosphates significantly / or at all from the water.

I know from several credible sources that this skimmer was able to bottom out previously high phosphates in larger tanks (300 gallons up). Any thoughts?

I cannot continue doing 30% weekly water changes, and I am looking for a serious solution to this problem (which, ideally, does not involve LC).

DOC Skimmer 9430 - Tunze

Hi-Tech für Aquaristik

www.tunze.com

 

[Slingfox]

I believe the science of skimmers has been around a long time so what about Tunze’s skimmer allows it to skim phosphates better than other skimmers. I have not been in the hobby long but it looks like the tech upgrades to skimmers in the last few years have all been pretty basic: DC motor, more controlability via an app, neck cleaner, light up skimmer body, sensors which help prevent overflow, auto drain feature, etc. None of these relate to the basic science behind the skimming process itself.

 

[Alexander1312]

I believe the science of skimmers has been around a long time so what about Tunze’s skimmer allows it to skim phosphates better than other skimmers. I have not been in the hobby long but it looks like the tech upgrades to skimmers in the last few years have all been pretty basic: DC motor, more controlability via an app, neck cleaner, light up skimmer body, sensors which help prevent overflow, auto drain feature, etc. None of these relate to the basic science behind the skimming process itself.

Agreed. Does the basic science say it does not remove phosphates?

I just wanted to clarify, as I was not clear in my initial post. I am not saying that Tunze skimmers do and other skimmers do not. I know from this skimmer that it does a very good job (apparently), given the pump they put in it (which is why it is so expensive). This started me rethinking skimmers again (and their settings) if phosphate reduction is my core objective.

 

[L/B Block]

The science say it does -but whether it removes enough is the question- skimming alone has never gotten my PO4 low enough.

Maybe the beast above does -I can’t say

 

[tribbitt]

Reefs.com says skimmate has around 4700 ppm phosphate so to me that sounds plausible. But how much are you actually intending to skim lol

Elemental Analysis of Skimmate: What Does a Protein Skimmer Actually Remove from Aquarium Water?

Department of Chemistry, The Pennsylvania State University, University Park, PA 16802. The chemical/elemental composition of skimmate generated by an H&S 200-1260 skimmer on a 175-gallon reef tank over the course of several days or a week had some surprises.

reefs.com

 

[Alexander1312]

The science say it does -but whether it removes enough is the question- skimming alone has never gotten my PO4 low enough.

Maybe the beast above does -I can’t say

That is exactly the issue I have. Because it seems they do not, folks are looking for different methods, adsorber, lanthanum, etc.

I always thought setting the skimmer (too) high does not make it more effective as it relates to phosphate (or nitrate for that matter). But it looks like if you are adding one of the most efficient and effective hobby grade pumps available to a skimmer, i.e., the Tunze Stream 3, it might have this effect.

So my thought was that maxing out my existing skimmer’s capabilities might give me a similar effect - I am currently only running it at 50% speed to get the darker skimmate.

 

[Alexander1312]

Reefs.com says skimmate has around 4700 ppm phosphate so to me that sounds plausible. But how much are you actually intending to skim lol

Elemental Analysis of Skimmate: What Does a Protein Skimmer Actually Remove from Aquarium Water?

Department of Chemistry, The Pennsylvania State University, University Park, PA 16802. The chemical/elemental composition of skimmate generated by an H&S 200-1260 skimmer on a 175-gallon reef tank over the course of several days or a week had some surprises.

reefs.com

Nice!

 

[PjFish]

Reefs.com says skimmate has around 4700 ppm phosphate so to me that sounds plausible. But how much are you actually intending to skim lol

Elemental Analysis of Skimmate: What Does a Protein Skimmer Actually Remove from Aquarium Water?

Department of Chemistry, The Pennsylvania State University, University Park, PA 16802. The chemical/elemental composition of skimmate generated by an H&S 200-1260 skimmer on a 175-gallon reef tank over the course of several days or a week had some surprises.

reefs.com

I assume it may be high since it’s like testing concentrated frozen OJ!

 

[PjFish]

Here’s a great thread related to your topic I read a while back @Alexander1312
Pay particular attention to Randy Holmes-Farley’s responses since he’s a guru of reef chemistry!

POLL: Do skimmers remove nitrate and phosphate?

True, but I tried to ask if it directly removed those inorganic nutrients. I could have worded it better. Seems clear to me. A skimmer does not remove them. It may result in lower tank levels, but that is a different question. :)

www.reef2reef.com

 

[Alexander1312]

Here’s a great thread related to your topic I read a while back @Alexander1312
Pay particular attention to Randy Holmes-Farley’s responses since he’s a guru of reef chemistry!

POLL: Do skimmers remove nitrate and phosphate?

True, but I tried to ask if it directly removed those inorganic nutrients. I could have worded it better. Seems clear to me. A skimmer does not remove them. It may result in lower tank levels, but that is a different question. :)

www.reef2reef.com

A guru . So unless I misunderstand, Grandmaster Randy says, the beloved wet skimming method is a stupid idea?

 

[PjFish]

A guru . So unless I misunderstand, Grandmaster Randy says, the beloved wet skimming method is a stupid idea?

Theres no mention of wet skimming in the thread ? But he will give you his opinion Im sure if you ask him..
My opinion wet skimming just stretches out water changes since the skim mate is really diluted and your removing more water then actual skim. Some reefers just use their skimmers ( wet skimming ) doing smaller water changes more frequently..

 

[Alexander1312]

Theres no mention of wet skimming in the thread ? But he will give you his opinion Im sure if you ask him..
My opinion wet skimming just stretches out water changes since the skim mate is really diluted and your removing more water then actual skim. Some reefers just use their skimmers ( wet skimming ) doing smaller water changes more frequently..

Yes, I know there was no mention of this, I have been just trying to think this further.

Why do you think folks do not just water changes but go the more cumbersome route and use the skimmer for this? This is a genuine question, not a rethorical one. I thought it was to remove extra Nitrate and Phosphate from the water relative to what would be removed by water changes. According to RHF, this would not be achieved by this method. Again, maybe I misunderstood the purpose, so for discussion only.

 

[JVU]

Alex @Alexander1312 I think part of the confusion is just precision of term use. So indulge me giving a little background. Skimmers remove dissolved molecules that adhere to the surface of bubbles because they have one side that is attracted to water and one side that is repelled by it. The term for this is amphipathic. Any water surface, and especially the surface of a bubble, gives them this preferred environment, water on one side and air on the other. By being there, these molecules also stabilize the tiny bubbles so they don’t pop as quickly and make a foam. So a skimmer collects these molecules in the foam. Thicker skimmate has more organics and less water, wetter skimmate has more water. Skimming wet removes more organics per amount of time, at the expense of losing more water. Which is fine if you’re doing a water change with it anyway.

Amphipathic molecules in our tank are mostly organic in origin, and largely proteins. So lots of N and P (as well as C and others). So when you skim you are removing this stuff. If these complex organics are not skimmed out, they break down into stuff like nitrate and phosphate. Nitrate, nitrogen, phosphate and phosphorus themselves are not amphipathic so they don’t skim out directly.

So to say that skimmers don’t remove phosphate is technically correct, they remove the organic waste precursors of phosphate. So effective skimming does lead to lower phosphate levels. Other processes in the tank like coral and algae life/growth also remove phosphate and precursors.

Regarding that specific skimmer, I don’t have any experience or insight. But certainly a more effective skimmer would be more effective at lowering phosphate.

 

[Alexander1312]

Alex @Alexander1312 I think part of the confusion is just precision of term use. So, indulge me in giving a little background. Skimmers remove dissolved molecules that adhere to the surface of bubbles because they have one side that is attracted to water and one side that is repelled by it. The term for this is amphipathic. Any water surface, and especially the surface of a bubble, gives them this preferred environment, water on one side and air on the other. By being there, these molecules also stabilize the tiny bubbles so they don’t pop as quickly and make a foam. So a skimmer collects these molecules in the foam. Thicker skimmate has more organics and less water, wetter skimmate has more water. Skimming wet removes more organics per amount of time, at the expense of losing more water. Which is fine if you’re doing a water change with it anyway.

Amphipathic molecules in our tank are mostly organic in origin, and largely proteins. So lots of N and P (as well as C and others). So when you skim you are removing this stuff. If these complex organics are not skimmed out, they break down into stuff like nitrate and phosphate. Nitrate, nitrogen, phosphate and phosphorus themselves are not amphipathic so they don’t skim out directly.

So to say that skimmers don’t remove phosphate is technically correct, they remove the organic waste precursors of phosphate. So effective skimming does lead to lower phosphate levels. Other processes in the tank like coral and algae life/growth also remove phosphate and precursors.

Regarding that specific skimmer, I don’t have any experience or insight. But certainly a more effective skimmer would be more effective at lowering phosphate.

That is very helpful, John, thank you.

So wet skimming removes more precursors and effectively lowers nutrients overall from the water measured (at a later point) as nitrate and phosphate. It will not remove phosphate and nitrate that have already separated/broken down specifically.

Also, I appreciate the conclusion that a more effective skimmer would be more effective in lowering phosphates, which is the main opinion I am looking for.

Yet, I am still confused about two related things:

1. If the above is correct, why is there a pervasive recommendation in the hobby to go for a right-sized skimmer, specifically one that is not (!) oversized? And often communicated overskimming concerns, which I believe also relate to the fact that trace elements are pulled out from the water disproportionately.

2. What constitutes an ‘effective’ skimmer? A more powerful pump and a larger body? Can I scale the skimmer effect by getting the biggest skimmer that fits into my sump and run this at maximum speed, or are there diminishing returns from this? Is there a limitation with skimming, which, e.g., cannot get the water below a certain N and P level?

 

[JVU]

I’m not sure I have direct answers to your followup questions. One additional consideration that might help is that a skimmer’s rate of pulling out amphipathic organics depends not only on the skimmer itself and its settings, but also the concentration of the organics in the water. So if you have lots of organics, any skimmer will pull a lot out. As you get less and less left in the water, the rate of removal also goes down and it takes a more effective and properly tuned skimmer to keeping pulling out organics. So there certainly are diminishing returns as you said.

When people talk about sizing a skimmer and the risk of overskimming, they are talking about the balance of skimming out excess organics while not skimming out so much that it causes problems. You need some organics, N, P, etc recirculating through the nutrient cycles in your tank. It’s technically true that you can indirectly skim out some trace elements, or even major and minor elements for that matter, IF they adhere to organics and the organics are skimmed out. The major/minor/trace elements themselves are not amphipathic and don’t skim out directly. How much they adhere and get removed is a matter of debate and I don’t have an answer for you except that my impression is that it’s negligible compared to the benefits of a skimmer. I don’t see any reason why an oversized skimmer would disproportionately pull out more trace elements since they don’t skim out on their own.

 

[Alexander1312]

I’m not sure I have direct answers to your followup questions. One additional consideration that might help is that a skimmer’s rate of pulling out amphipathic organics depends not only on the skimmer itself and its settings, but also the concentration of the organics in the water. So if you have lots of organics, any skimmer will pull a lot out. As you get less and less left in the water, the rate of removal also goes down and it takes a more effective and properly tuned skimmer to keeping pulling out organics. So there certainly are diminishing returns as you said.

Very interesting, and it opens up another rabbit hole for me .

Is having higher NO3 and PO4 the equivalent to having higher organics, or is the issue more differentiated, that I might have lower organics in the water but still higher N/P parameters? Could be a stupid question but I just wanted to see if there is something which can prohibit an oversized skimmer to help getting to lower N/P values.

Also, I wonder if ozone could play a (negative) part in this, by destroying organics before they can be removed by the skimmer, limiting its effectiveness. Some claim skimming with ozone is improved, others claim it got worse. I am certainly more in the latter camp, but I wonder if there is a biological explanation for this.

When people talk about sizing a skimmer and the risk of overskimming, they are talking about the balance of skimming out excess organics while not skimming out so much that it causes problems. You need some organics, N, P, etc recirculating through the nutrient cycles in your tank. It’s technically true that you can indirectly skim out some trace elements, or even major and minor elements for that matter, IF they adhere to organics and the organics are skimmed out. The major/minor/trace elements themselves are not amphipathic and don’t skim out directly. How much they adhere and get removed is a matter of debate and I don’t have an answer for you except that my impression is that it’s negligible compared to the benefits of a skimmer. I don’t see any reason why an oversized skimmer would disproportionately pull out more trace elements since they don’t skim out on their own.

This part is also interesting, but more a side conversation at this point. Fauna is claiming that their trace solutions are better able to be absorbed by animals, aka corals (similar to claims for human vitamins and minerals) due to their connection to organics (often polymers, but potentially others, it is apparantly a trade secret). This could mean that these would be more likely taken out by the skimmer and specifically overskimming. Maybe I am not getting the logic right here, but just trying to connect some dots of my knowledge fragments.

Overall though, having higher N/P seems to indicate to max out the skimmer potential first before anything else, not necessarily going for the darker/drier skimmate but being ok with wetter skimming and its positive and (potentially negative) consequences.

 

[Alexander1312]

Added a poll, just for fun.

 

[JVU]

Very interesting, and it opens up another rabbit hole for me .

Is having higher NO3 and PO4 the equivalent to having higher organics, or is the issue more differentiated, that I might have lower organics in the water but still higher N/P parameters? Could be a stupid question but I just wanted to see if there is something which can prohibit an oversized skimmer to help getting to lower N/P values.

NO3 and PO4 are not organics, since organics have carbon in them as well. But in our systems they come from broken down organics, so certainly are related. Also N isn’t the same as NO3 and P isn’t the same as PO4 since they can be in different forms. Note that ICP testing looks at the elements (eg N and P) and not the molecules (NO3, PO4). Some of the tests give extrapolated concentrations to try to be more useful.

To answer your question, you could have a situation where organics are highly skimmed out but your NO3 or PO4 are still elevated, if they are coming from other sources like supplements or preservatives added to fish food for example. Or if you just have a lot of organics coming through the system so that even though you are skimming a lot out you are also having a lot broken down too (ie feeding a lot). Those scenarios are pretty common in reef tanks, which is why people who skim also often use GFO or lanthanum.

Also, I wonder if ozone could play a (negative) part in this, by destroying organics before they can be removed by the skimmer, limiting its effectiveness. Some claim skimming with ozone is improved, others claim it got worse. I am certainly more in the latter camp, but I wonder if there is a biological explanation for this.

I don’t know much about ozone treatment.

This part is also interesting, but more a side conversation at this point. Fauna is claiming that their trace solutions are better able to be absorbed by animals, aka corals (similar to claims for human vitamins and minerals) due to their connection to organics (often polymers, but potentially others, it is apparantly a trade secret). This could mean that these would be more likely taken out by the skimmer and specifically overskimming. Maybe I am not getting the logic right here, but just trying to connect some dots of my knowledge fragments.

What you mention is possible. Without knowing what FM is conjugating to I couldn’t say anything useful. If they are conjugating to something that is amphipathic then it will get at least partly skimmed out.

Overall though, having higher N/P seems to indicate to max out the skimmer potential first before anything else, not necessarily going for the darker/drier skimmate but being ok with wetter skimming and its positive and (potentially negative) consequences.

Sounds reasonable

 

[Alexander1312]

NO3 and PO4 are not organics, since organics have carbon in them as well. But in our systems they come from broken down organics, so certainly are related. Also N isn’t the same as NO3 and P isn’t the same as PO4 since they can be in different forms. Note that ICP testing looks at the elements (eg N and P) and not the molecules (NO3, PO4). Some of the tests give extrapolated concentrations to try to be more useful.

Sorry, yes, I was aware of this. N and P were short for NO3 and PO4 in my write up, but should have been clarified, since we were talking in more detail.

To answer your question, you could have a situation where organics are highly skimmed out but your NO3 or PO4 are still elevated, if they are coming from other sources like supplements or preservatives added to fish food for example.

Yes, this point deserves closer assessment. I am using low phosphate frozen food, but the dry food could have more phosphate, i.e., TDO. I wonder if this is the point connected to RHF statement were this type of phosphate is 'unskimmable', and can only be removed through water change or artificial means (GFO/LC).

Or if you just have a lot of organics coming through the system so that even though you are skimming a lot out you are also having a lot broken down too (ie feeding a lot).

This would mean the skimmer is underpowered for its job at hand, and could be resolved by getting a stronger skimmer, I assume.

Those scenarios are pretty common in reef tanks, which is why people who skim also often use GFO or lanthanum.

Understand, and I am still trying to minimize the need for this, but I am also using a type of iron based adsorber in a reactor at the moment to lower PO4.

I don’t know much about ozone treatment.

Not many people do, which it why it is hard to find an answer to the impact of ozone in skimmers. It looks like ozone divides longer organic molecules into shorter ones and if these become too short, they might no longer be effectively skimmed out. At least that is the semi-factual working assumption of the problem. I have been thinking of using an ozone reactor instead and keep the skimmer separate from the ozone treatment.