Does the "head" height of a skimmer matter? I mean depth of the skimmer in the sump.

Discussion in 'Equipment' started by Vincerama2, Jan 31, 2017.

  1. Vincerama2

    Vincerama2 Evil Overlord

    I've swapped out my trusty (but too small) AquaC EV-120 skimmer for a used (but clean and soooo well built) Skimz Monster 203 skimmer. I was shocked, amazed and very pleased that the new larger skimmer fit exactly in the small space that the old skimmer (with its external pump) sat. The clearance above the skimmer is maybe an inch and a half and a quarter inch is all that's needed to remove the collection cup.

    What I've noticed is that the skimmer sits "deep" in the sump AND that I have to keep the DC pump set to its lowest setting or else ... my cup runneth over.

    I think if I raise the skimmer up a bit (the pump sits inside the skimmer body) it would create more head pressure as the pump would have to push the water more upwards above the sump's water level. And then maybe I could open the output of the skimmer if need be to avoid the water column going up into the collection cup.

    Now my actual question is .... does that do anything? Will running the pump harder help the skimmer at all? Or will the subsequent adjustment of the out-flow valve and air valve basically negate any possible benefit of having water pumped in harder? I mean it's only pumping slightly harder to compensate for the slight increase in head pressure to get the water column up to the same spot.

    Does it matter at all how deep the skimmer sits? If it makes no difference then I'd much prefer to let the skimmer sit deeper, so I can save 1 cent/month in electricity for the pump at the lower setting (and maybe extend the pump life)

    Scum production is currenlty neither exciting nor disappointing. Pretty much the same as the old skimmer :/ though maybe more energy efficient and certainly quieter.


  2. roostertech

    roostertech reef noob

    (foreword: I only used skimmer for three weeks so far, thus I might be talking out of my ass)

    Deeper water level -> more pressure on output side -> your bubble level is raised higher
    Yep the same effect can be achieved by closing your output gate valve

    The point of cranking up your DC skimmer is to produce more bubble -> more skimming action

    I would leave the gate valve wide open, raise up the skimmer to the manufacturer spec range, crank it up bubble to where you think is appropriate for your bioload, it should not be overflowing yet. And then dial in the gate valve to raise bubble level to where you want it to be (wet vs dry skim)
    Coral reefer likes this.
  3. Coral reefer

    Coral reefer President

    Every skimmer has a sweet spot for the depth of water it operates in. I'm sure you can google it for yours.
  4. rygh

    rygh Supporting Member

    The depth can also have a subtle effect on the air intake.
    More depth = more pressure = less venturi effect.
    That is even more pronounced if you turn down the pump.

    Opinion: The main issue is dwell time versus flow.
    Shallow = less flow, more dwell time.
    Deep = more flow, less dwell time.
    The sweet spot depends on the skimmer and percentage of pollution in the water.
    If your tank is fairly clean, I think you might want more dwell time. Slightly.

    I also think that the manufacturer (hopefully) tested it far more than we will, so what they
    say for depth is probably a good idea.

    So my suggestion:
    1) Keep pump near max.
    2) Stay in factory recommended range, perhaps slightly toward shallow end.
  5. Vhuang168

    Vhuang168 Supporting Member

    You don't want to max out the pump. Higher flow (while will generate more bubbles) also decreases dwell time. You want foam, not bubbles that burst at the top.

    Here is what the Scott Lief over at Bubble King suggests

    "Increasing the pump speed sends more water into the skimmer body. This decrease contact time, increases the bubble size and makes the bubbles tend to burst at the surface instead of generating good foam. Ideally you want to set the pump speed so that you are getting the most dense foam possible and then use the water level in the sump and or close the wedge pipe to increase the foam level inside the skimmers neck. By increasing the pump speed, it will raise the water level up but you will tend to get more water removal and less dissolved organic removal. Again, the idea is to use the pump speed to achieve the most dense foam that fills the neck as much as possible. If your not making foam, you're not removing as much of the DOC's as you can or you just don't have enough DOC's to generate a good foam head. In you case, that will be an issue no matter what but the slower pump speed (between 28 & 32 watts) will be the best setting for a 200 sized skimmer. You just need to use the pumps speed to find what works best for your load. "

    So start at manufactuer's recomended depth, wedge pipe 1/4 closed (3/4 open). Adjust the pump will you get the densest foam, then move the water level up or down by playing with either the water level the skimmer sits in or if not possible, the wedge pipe. Skimmer level in sump is a gross adjustment while the wedge pipe is finer.
  6. rygh

    rygh Supporting Member

    Raising the skimmer body and reducing the pump speed both reduce flow / increase dwell time.
    So that is basically the same either way.

    A slower pump seems like it would not generate bubbles as well though.
    Key being that the needle-wheel is going slower, so not chopping the bubbles as much.

    But a slower pump also saves power of course.

    Well, I have never used a DC skimmer, so not like I can say they are wrong.
    I just like to understand the physics.
  7. yellojello

    yellojello Supporting Member

    When you say deep, what is the distance from water level to bottom of skimmer? The SM203 manual suggests between 7"-9.5"

    Also, is your Micro-Adjustable gate valve fully open or closed? Air valve fully open? Perhaps need time to break it in.

    I have the smaller SM201, sitting about 8.5" from water line to bottom of skimmer. I like to dry skim, so the microbubbles is set right below the white collar... usually they say in the neck between the collar and the collection cup.
  8. Coral reefer

    Coral reefer President

    Some have air intake adjustments now too. This can Ben used to increase or decrease air draw into the mix.
  9. Vincerama2

    Vincerama2 Evil Overlord

    Yes, I read the "manual" (ie two pages) last night. I raised the skimmer 1 and a quarter inches, which is the max before I can't take the cup off the skimmer. The water level now sits around 9.5" from the bottom of the skimmer I got lucky with the clearance as it Juuuuust fits.

    That allowed me to (with the gate FULLY opened), increase the pump speed to 50%. I then opened the air valve about 1/4 turn. Then I adjusted the gate until the TOP of the resulting bubbles (bubble to air interface) was halfway up the neck, as per the instructions. After some time, the bubble interface raised a bit and I adjust the gate to bring it down a touch more, then left it to skim. We'll see how it is when I get home tonight.

    The manual says to use the air valve to adjust for wetter or dryer skimmate, I assumed that meant using the air level to adjust bubble interface height ... moving it lower (allowing more air) to get a dryer foam and moving it up (allowing less air) to make it wetter.

    If I find a sweet spot, I'll leave it. OR I'll reduce the pump speed by one tick and close the output gate to compensate to save a few cents worth of power.

    BUT I'll do that after I give the skimmer a week or so of skimming.

    No need to break it in, it was on an ex-reefer's tank before I bought it from him. (ie it needs to adjust to my tank, but I don't need to wait until the manufacturing residue is washed off)

  10. Coral reefer

    Coral reefer President

    Less pump speed more air if you can is my preference
  11. Coral reefer

    Coral reefer President

    Def no more water flow through than return pump flow through the sump.
  12. Vincerama2

    Vincerama2 Evil Overlord

    Yes I agree. I think more dwell time is better, slower water through skimmer. Plus more power efficient. I will tune accordingly after I see how it's running now.

    I think the bottom line for my situation (sky high nitrates) is that I'm not removing accumulated nitrate, rather than this (or my previous) skimmer not removing enough crap, though a combination of both doesn't help. Hopefully this helps. I've ordered a biopellet reactor to help, and have almost 44 gallons of salt water ready to change. I may also just put a container of sand in the sump too as a makeshift, and tiny DSB for what it's worth.

    I might have some "nitrate sponge" stuff somewhere I can try too.

    Thanks for the skimmer tips guys!

  13. Coral reefer

    Coral reefer President

    Skimmer prevents nitrates from hapening by removing organic matter before it breaks down into nitrates, but doesn't remove them once they are there. Do you have very old nasty sand? If you pull a rock out into a bucket of tank water and shake it does a ton of stuff come out? If so, I'd consider changing out your sand and or rock.
    IMO if you want a magic bullet type fix like I'm thinking you are hoping the biopellets would be I would try a sulphur denitrator first.
  14. rygh

    rygh Supporting Member

    The only thing that reliably gets rid of high levels of both nitrates + phosphates is massive water changes.
    Denitrators and such work, but more on nitrates than phosphates, and at your high levels, can cause all sorts of slime and other problems.
    As for the BEST long term denitrator ... hahah I am not going there.
    +1 on Mike's advice. But be very careful disturbing a dirty sand bed.

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