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Thread: scrubber effects on alkalinity?

  1. #1

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    scrubber effects on alkalinity?

    I searched long and hard and couldn't find a thread dedicated to this:

    How badly does an algae scrubber affect alkalinity? I found many mentions that theoretically algae growth can consume bicarbonate, but there are extremely few people complaining about low alk. If I install an algae scrubber, is my ca/alk balance going to be thrown way off? what can i expect? Is it really any better with an upflow design?

    thanks!

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    After a while when you have really good growth. Garf figured out that if you put bubbles through the screen it reduces this.

    I added 1oz of alk per week to compensate.

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    Welcome.

    Most people don't have strong scrubbers so they don't consume any alk. But if you have strong growth quickly, it will pull alk down a few points in a week. A tablespoon or two of baking soda puts it right back up.

    Of course even a strong scrubber will slow down if nutrients are brought low in the tank and you don't start feeding more.

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    Remember that raw baking soda will lower pH, baked baking soda will raise it. IMO the latter is better, or a blend of each. Google it and read up.

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    it seems like alk drop isn't a major problem. when algae consume bicarbonate, they release hydroxide. that hydroxide contributes to the carbonate - bicarbonate equilibrium and the net gain or loss of alkalinity is zero. It is a cycle. The algae is not consuming the alkalinity.

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    Biogenic decalcification

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    no, the minor release of hydroxide is not enough to cause any calcium carbonate precipitation in a reef tank. The hydroxide will equilibriate back into the system long before the tank get so out of whack that you get precipitation. plus, that would be a balanced calcium and alkalinity sink. the often-discussed phenomenon is a drop only in alkalinity.

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    Quote Originally Posted by Garf View Post
    Biogenic decalcification
    Google this and read up. If this wasn't the case, then people would not be complaining that their scrubbers are sucking down their alk levels.

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    like i said, that is a freshwater phenomenon. a little extra hydroxide is not going to cause anything in a marine environment. plus, decalcification would cause a balanced depletion of Ca and Alk, like I said.

    i would love it if someone could propose a chemical mechanism for alkalinity depletion by non-calcifying algae in a marine environment.

  10. #10
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    Quote Originally Posted by rwb500 View Post
    like i said, that is a freshwater phenomenon. a little extra hydroxide is not going to cause anything in a marine environment. plus, decalcification would cause a balanced depletion of Ca and Alk, like I said.

    i would love it if someone could propose a chemical mechanism for alkalinity depletion by non-calcifying algae in a marine environment.
    Have a look at this;
    http://algaescrubber.net/forums/show...ll=1#post30279

    May be because only 20ppm calcium is precipitated, compared to a whopping 2.8dkh alkalinity. Dunno about every else but my calcium test is crap, alkalinity test not so bad. Perhaps the calcium drop just gets missed. In that thread there's a few links that show photosynthetic calcium carbonate precipitation occurs in the ocean. In our tanks, it may well be confused because increasing the pH to 8.4 (a known effect of photosynthesis) also increases precipitation from corals and calcifying algae.

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