Water change vs top up?

Discussion in 'Beginner Discussions' started by Ivyalt, 15 Apr 2012.

  1. Ivyalt

    Ivyalt

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    Hi all, just started my marine and learning fast thanks to you guys! Nb:FOWLR TANK

    My questions and statements:

    1. Am I right in saying that my 6ft tank,850 liters (open top and sump) can evaporate 75
    liters per week in winter, +- ? I am estimating now.

    2. That being the case I theoretically do a water change of 6.2% per week anyway.

    The problem is that the RO contains no good minerals? (good for nitrates though)
    Also the RO has a low ph thus effecting/lowering my ph.

    3. Should one at least do an equivalent change per week with RO salt ph mix (water
    change rules) to keep the ph stable and minerals where they should be?


    How do you guys do it?
     
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  3. 2balive

    2balive

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    Hi

    I do not have a feeling feeling for evaporation rates in open top tanks anymore, but in terms of top-up counting for water changes, I am afraid not. Only "pure" water evaporate and it does not take out any of the nitrates (or any other impurities). It would be a good school project to test for this. So before you top-up, your Nitrates levels will actually be more concentrated due to evaporation. Top-up only brings your nitrates levels back to what it was before the evaporation took pls.

    Also as you said, top-ups can't replace your used/lost elements and water changes are the easiest form of doing this. I however found that even with 15% weekly changes I still have to dose calcium, alkalinity and magnesium in addition to the water-changes.

    I know that some people use kalkwasser to compensate for this, as for top-ups, but you will have to read up about this as I think it requires some tweaking of he system re skimming and PH.
     
    Last edited: 15 Apr 2012
  4. ScottK

    ScottK

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    When water evaporates it leaves the minerals behind, RO is used to top up to keep the correct balance. If you top up with salt mix eventually your salinity and mineral levels will be too high or out of balance.

    Depending on what is in your tank the uptake of certain minerals may be high which is why people dose additional calcium, magnesium, kalk etc.
     
  5. ScottK

    ScottK

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    To add to the above evaporation can be unique to ever tank depending on various factors such as lighting, fans, pumps etc.

    Tanks for example with multiple metal halide lamps and fans running to keep them cool can have a much higher rate of evaporation than a tank with T5's or LED's. You will need to check your tanks needs and test for use of critical elements for your stock to find what works best for you, I don't think there is any set formula to work with unfortunately.
     
  6. RiaanP

    RiaanP Moderator

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    Yes easily 10% per week. But it depends on so many factors, like room draughts, fans, scrubbers, type of lighting....

    No, still do your 10%. You should not do such a big top up that it affects your PH. The less each top up volume is, the more stable your system.


    Yes, mix the salt powder with RO water at least a day earlier. Small circulation pump to help.

    Take into account that you loose a bit of salt in the skimmer cup. So in theory your salinity over time will go down a bit. So you need to check your display salinity and the salinity of the new salt mixture. If display do drop, you can make the new mix slightly stronger. Get a refracto meter.

    On a 10% water change, the temperature difference is not that crucial. a 5 degree difference in temp would impact 0.5 degrees in the system. So close is OK, do not need to be exact. Unless you dump the new water directly into the display on top of some corals and fish.
     
    Last edited: 15 Apr 2012
  7. Ivyalt

    Ivyalt Thread Starter

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    So...In short this is what one should do?

    Appart from +- 10% evaporation per week (top up with RO) one should do a +- 10% water change (pre salt mix) to replensh all elements...testing as all systems differ off course.

    Any other inputs in ths regard will be greately appreciated?
     
  8. Viskop

    Viskop

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    I also understand that only pure water evaporate and salt, etc are left behind, but where does the "salt crust" you get inside your lid over time, comes from then?
     
  9. RiaanP

    RiaanP Moderator

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    Salt spray is a form of salt lost. But you should not have excessive salt spray.

    And if really technical, the skimmer do remove other minerals as well. Not just the fatty protein and DOC. But is such small quantities per week. That it is not needed to talk about it.
     
  10. Viskop

    Viskop

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    That makes sense, thanks.
     
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