When and why should you do a water change?

Discussion in 'Reef Chemistry' started by fishy408, May 14, 2018.

  1. fishy408

    fishy408 Supporting Member

    When I first started with my reef tank, I had plans! I wanted to have enough corals where a 30% water change once/month would replenish the needed minerals.

    After cycling, I did a 90% water change.
    1 month later, I did a 30% water change...Why did I do a water change? I'm not really sure, it was according to schedule and something I just usually do out of habit.

    Currently I have very few corals as I'm taking my time and letting the tank settle while trying to find a balance.

    • DKH (10.9), Calc (450), Mag (1500)
    • PO4 is undectable by Selifert
    • Nitrate has been descreasing as the skimmer and algae reactor picks up.
      • POR (.03 or less)
      • Nitrate (5)
    • Once I have enough Corals to deplete the (DKH, Calc, Mag), then I would consider dosing something.
    If your water readings are good, why do a water change? Am I missing something?
  2. rygh

    rygh Supporting Member

    It is difficult to test all of the elements in the water.
    Water changes are an easy way to ensure most other minerals/etc are good.

    Plus, a good way to siphon out detritus.
    fishy408 likes this.
  3. fishy408

    fishy408 Supporting Member

    My first batch of Chaeto kinda died. The second set of Chaeto seems to be doing well and growing.

    For the second batch of Chaeto, I turned off my phosphate reactor.

    If water changes descrease nitrates and phosphates, wouldn't it affect my chaeto growth or maybe the chaeto may starve and die off.

    Just thinking out loud :)



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    Last edited: May 14, 2018
  4. grizfyrfyter

    grizfyrfyter Reef Geek 3D Printed

    You definitely can get away with not doing any water changes if your nutrient export is on point but it's like grocery shopping in the dark. You don't really know what's in the tank other than the stuff we can test for as Hobbyist. Even the trace elements test are rare.

    If you don't want to do water changes, you can do the Triton / ATI tests and supplement system. The test measure 40 something elements and will tell you what to dose and how much to bring things in line. This will not save you money ($40-$50 a test and lots of dosing supplies) or time.
    fishy408 likes this.
  5. fishy408

    fishy408 Supporting Member

    I have a water change system in place that allows me to change about 30% of the water in about an hour. 1 hour a month is definitely doable. I was just curious why and when I should do it.

    If water params are good the reasons are:
    1. remove detritus
    2. replace elements that are hard or impossible to detect by hobby test kits.
    I did read up on the Triton systems, but just read so many complaints about the core elements being out of stock :-(.
  6. Kensington Reefer

    Kensington Reefer Supporting Member

    The solution to pollution is dilution

    30% or more every 10 days
    Remove pollutants
    Replenish elements
    No chemistry tests
    No chasing numbers
    Feed the fish an corals well and often

    Old fish and corals
  7. rygh

    rygh Supporting Member

    Also note:
    Automatic water EXCHANGE systems are pretty easy to set up.
    A salt water tank, two peristaltic pumps, and a timer are about it.
  8. grizfyrfyter

    grizfyrfyter Reef Geek 3D Printed

    Yes. But water changes are extremely inefficient.

    Say your trying to reduce nitrates. A 30% water change (about 55g in my tank) will take a tank from 20ppm to 14ppm. Another immediate water change brings it down to just under 10ppm. So to reduce nitrates by half, I've changed 110g of water.

    Now, to maintain chemistry, your new water has to be HIGHER than what your goal is which means you buy a high level salt, like red sea coral pro, which is very expensive, or you dose the new water, which requires testing.

    I'm not saying water changes don't work but the cost of weekly, or even bi-weekly water changes is quite high. Not to mention the time involved.
  9. fishy408

    fishy408 Supporting Member

    I read up on automatic water changes and thought it would be cool to automate. I would have to run the pipe from the garage (salt water storage) through the crawl space and up through the wooden floors to reach the display tank.

    I asked the wifey, wouldn't it be cool if the water changes can be automated. All we need to do is drill a hole through the wooden floors.

    Her response was, "Do you remember when....." , thats when I knew it's not going to happen. :)
    grizfyrfyter likes this.
  10. Kremis

    Kremis Supporting Member

    I personally water change every week. Helps with nutrients, replenishes trace elements, and just in general I think helps the system. I figured out the cost of salt for doing this to be about 10$ a water change (30 gallon water changes) so overall not that high. I also have a system setup where a water change takes me about 20 minutes total and not a lot of work, so they arent that big of an issue. I also have a mostly zoa tank, and personally believe that zoas do well when trace elements are replenished frequently as correct me if im wrong but no one really knows for sure what they "use up".
    grizfyrfyter likes this.
  11. rygh

    rygh Supporting Member

    Drill through the floor inside the walls.
    Put a hole in the wall, and a standard empty receptacle, like you would for a plug.
    So when covered with a blank faceplate, looks totally normal.
    Then drill a hole from below, in the wall below that.
    Finding the exact right spot can be tricky of course...
    Coral reefer likes this.
  12. Flagg37

    Flagg37 Officer at large

    I think of water changes as another tool in the toolbox. I haven’t done one in almost a year. I have a fairly large fuge that I grow chaeto in for nutrient export. I even took out my skimmer. I use kalkwasser to replace major elements and the Red Sea trace colors for the minor and trace elements. If things were to get wonky for some reason a large water change is almost always beneficial.
    grizfyrfyter likes this.
  13. Rostato

    Rostato Supporting Member

    The biggest reason to do water changes is for trace element replenishment...
  14. Reefatosis

    Reefatosis Supporting Member

    For sure.....the solution to pollution is dilution

    Don’t forget allelopathy and other forms of coral war
    Don’t forget yellowing of the water column via dissolved organics that skimmers dont get
  15. rygh

    rygh Supporting Member

    On those particular problems, I would argue Carbon is better. (Or UV, or Ozone)
    Dilution through water changes is relatively slow.
  16. sfsuphysics

    sfsuphysics Supporting Member

    Unless of course the solution to pollution is absorption and removal by manual ... damn can't think of anything that rhymes with absorption.

    As Flagg said, it's a tool, not the only way of dealing with things and in fact is not a very good tool if it is the only tool you use.

    The "pollutants" are usually uneaten food decay products, often called nitrate and phosphate, many ways to remove those from a tank that don't involve dilution, in fact dilution is limited in the fact that you chop down a fraction (whatever your water change fraction was) and ultimately that's it, other methods can get closer to total removal, not saying that's necessary but if it is a goal of yours there are better ways than water changes.

    As for "trace elements", you can always dose "trace elements", and again compared to water changes it is something that you can control beyond a fraction. Lets say in your period between water changes 100ppb of "trace elements" get depleted because that's what all critters consume, now lets say fresh salt mix gives 1000ppb, so from day 1 to your first water change you got knocked down to 900ppb, you do a 25% water change and you throw away 25% of your water with 900ppb of these elements and add it back with 1000ppb, so 900*.75 + 1000*.25, and now your "trace element" count is.... 925ppb, so effectively gained 25ppb, the kicker is continuing this trend by next water change another 100ppb get used so you're down to 825, another 25% water change and 825*.75 + 1000*.25 and now your water is sitting at 868.75 bbp, ultimately you'll end up with 700 bbp. Now I just made up numbers for the sake of making up numbers to illustrate a point, and that's how much you can replenish with just water changes is going to always be less than the amount it originally had, and ultimately is dictated by consumption and percentage water change, if the consumption is only 50 ppb then it'll converge on 850bbp.etc. Now if your salt mix has an over abundance of a particular element then you can be perfectly fine, however if it doesn't then you will be forced to dose.
    grizfyrfyter likes this.
  17. rygh

    rygh Supporting Member

    For "trace" elements, it is unclear if actual levels matter much, as long as some is there.

    If the level of Calcium is cut to 1/4 natural sea water levels, coral growth will be impacted.
    If the level of Beryllium is cut to 1/4, does anyone care?
    The idea being - you only need a tiny bit, so it barely matters.
    And since you can go long periods with no trace additions, that tends to back that up.
    Of course, nobody knows for sure.
  18. rygh

    rygh Supporting Member

    Really good writeup here: http://reefkeeping.com/issues/2005-10/rhf/#14

    Note that you really should differentiate between minor and large water changes as well.
    Erin above mentioned 30% every 10 days.
    I do about 10% per month. Done nearly continuously.
    That is almost a factor of 10 difference, which fundamentally changes how it all works.
  19. grizfyrfyter

    grizfyrfyter Reef Geek 3D Printed

    That's what I was trying to say earlier, I think you made the point better than I did.

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