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.

Exactly how much baking soda were you adding?
I'd bet you simply did not add enough due to a miscalculation/misunderstanding..

Its highly unlikely that your alk consumption just magically increased as such a rate...

I used calculator: http://reef.diesyst.com/chemcalc/chemcalc.html

Since total water volume is about 10 g, I mixed 1.1 gram of baking soda to RO/DI and added to my tank. Instead of dumping all of them, I added one third of solution every two hours.

Yes you mis understood, here mix according to this page. And I would not raise your alk more than a half a point per day. http://www.reefkeeping.com/issues/2006-02/rhf/

Dear Cheapreef,

I don't understand which part I did wrong. I believe that the Randy's recipe #2 is basically the same thing with what I did. Can you specify a little bit?

I tried to raise 1 dkH/day; but actually it didn't increase that much. It stayed the same or decrease slightly.

If your not baking the baking soda and using it straight I would make at least 250ml of the recipe. 20grs of baking soda to 250ml of RO water. Mix this until it is 100% dissolved. Then you would add this to your tank, if your raising by .5 DKH you could do it all at once but even then I would most likely drip it in such a small tank. You would add 7.1 ML of this to your tank to raise by .5 DKH or so the calculator says.

I used baking soda without baking. So if I do the math, 20g/250ml*7.1ml*2=1.136g. That is exactly the same with what I mixed for 1 dkH increase. Then it means that I made alk solution with no error, right?

I mixed 1.1 gram to enough RO/DI and added one third of the solution to my tank, so it corresponds to 0.33 dkH at a time.

Do you have any idea why alk doesn't increase?

1 gram of baking soda should raise the dKH by 1 unit. You could try measuring a few minutes after dosing 1 dKH to make sure that the kit is working, assuming the kit is precise enough. What kit are you using?

It's possible in theory that the alkalinity is precipitating rapidly on some surface (like a heater), but that seems unlikely at the moment. If you see any whitish or tannish buildups, that'd be a sign, though.

Thanks bertoni. That sounds a reasonable explanation even though I don't see any noticeable buildup. The amount of buildup might be too small to be noticed but large enough to decrease Alk.

I used an API kit. Because my tank is in my office, I measured Alk several times in a day. I confirmed the kit can actually measure the alk increase after alk dose. By the way I added the alk solution to the area with most strong flow in the sump, where is around drain.

One day, for example, I dosed 0.33dkH as soon as I'm at work. It was 7dkH before dosing. Then I dosed the same amount two times more before I go home. So basically I tried to increase 1dkH in a day. Test kit says it increased to 7.5-8 dkH (API kit is not sensitive to .5 dkH change). Next morning I measured Alk, and it became 6.5dkH.

Alk was always 7dkh with kalk. However ever since the first extra alk dosing, Alk couldn't stay at a certain level with kalk anymore.

So if the alk drop is due to the buildup, will it saturate at some point? It has been a month since the first alk dose. I still see the alk drop if I don't supplement alk.




Sent from my iPhone using Tapatalk

Many tanks consume 2-3 dKH per day. My soft corals consumed that much due to coralline growth. I suspect that you are seeing normal consumption, but if the buildup becomes noticeable, that might indicate a need for a change in tactic. Is there sand in the tank? If so, is it becoming solid?

I set a dripper a couple of days ago and get relatively stable Alk. It's about 8 dKH now.

Since I added Alk supplement diluted in RO/DI, Kalk in ATO is also slightly less added. I did math. It turns out that Alk supply from Kalk is 1.35 dKH/day and now I'm adding about 1.5 dKH/day by Alk supplement. So my tank consumes 2.85 dKH/day now to sustain 8 dKH.

In conclusion, to raise Alk 7 dKH to 8 dKH, it's not like simply adding 1 dKH one time. While one time 1 dKH bump will bring 7 to 8 dKH, it will naturally decrease to 7 dKH again or even lower than 7 dKH in a day because of some CaCO3 precipitation or elevated growth. To sustain it at 8 dKH, I need to add 1.35 dKH/day more Alk supplement. Basically if you are using Kalk with full strength, you can't raise Alk without constant Alk supplement by extra.

Detailed numbers will be only valid for my tank. But I hope this information is useful to others who want to raise Alk.

Okay, that seems like a high, but reasonable, rate of consumption. Over time, if you supplement only alkalinity, the calcium level might drop, depending on the water change rate. Calcification consumes about 20 ppm calcium per 2.8 dKH, so it can take a while for the effect to show up. I'd watch the calcium level for a bit, but water changes might be enough to keep your tank in good shape.