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Unread 12/04/2017, 03:37 PM   #1
snowdrop6
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Join Date: Apr 2016
Posts: 29
alkalinity drops after baking soda dosing

These days, I have a hard time to make alkalinity stable in my 6 g reef tank with 4 g sump. This is how the problem started.

I do 2 g water change every 3 weeks. I use kalk in ATO for Alk and Ca. My parameter was fairly stable for long time (1.5 yrs old tank).

Alk: 7 (API)
Ca: >500 (Selifert) [I didn't correct it because it seems OK when I searched online]
Mg: 1350 (Selifert)
PH: 8.4 (API)
NO3: ~2-5 ppm (API)
PO4: ~0 (API)

A month ago, my ATO pump wasn't working for half a day, and the return pump also stopped for some reason. After fixing everything I measured parameters again. All were OK; but my alk was about 6 dkH (dropped from 7).

I thought it's a good time to raise my alk to 8-9 range because I have 2-5 ppm NO3 and wanted to accelerate coral growth a little bit. Coraline algae never grow in my tank, so, I thought raised alk might solve the problem too.


So I supplemented alk using baking soda. For three days, I dosed extra alkalinity of about 1 dkH/day. My alk was always at 7 dkH before, so I expected to be about 9 dkH (from 6 to 9). But it kept dropping ( Ca level dropped very quickly too). Despite of baking soda dosing, it's about 6.5-7 dkH range. I am puzzled. Why does the alk not increase even though I extra dose?

I believe this means my tank now needs extra alk more than 1 dkH/day on top of kalk. Is this normal? I suspect that when I raised alk, it triggered some extra growth of something like algae or snails in my tank, and then it boost alk consumption too. Is the right explanation? I just don't understand.

Now I can't make alk stable anymore with kalk. Is adding two-part dosing system the only solution here? Or is there any other way to try?

I'd like to keep alk about 9 dkH. I really appreciate your advice.


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