Dropping Alk

[DougSupreme]

I am having trouble keeping my Alk at an acceptable level. I have resorted to adding approx 3 tsp of baking soda or washing soda to the tank to restore my alk levels. Calcium is in the upper 400s. It was my understanding that organisms use alk to process Calcium. If this is correct, my calcium should also be dropping, which is not the case. I'm getting tired of constantly supplementing Alk. I'll feel much better when everything is equalized and I can just add Kalk.

BTW the only organisms I have in my tank that would use Calcium is coralline, Neomeris (calcareous algae), and some small tube worms. There may be more, but they are unbeknownst to me.

[mhurley]

[moved]

[Randy Holmes-Farley]

It was my understanding that organisms use alk to process Calcium. If this is correct, my calcium should also be dropping, which is not the case.

Most likely, you just haven't noticed it yet. The calcium appears to drop much more slowly. A big drop in alkalinity (1 meq/l or 2.8 dKH) is acccompanied by a drop of only 20 ppm in calcium when forming calcium carbonate. 20 ppm Ca++ is likely within the noise of most calcium kits.

Are you adding limewater now?

How old is the tank?

There are a few other processes that deplete alkalinity, one of which is the nitrogen cycle proceeding to nitrate and stopping there. That can be significant during curing of live rock.

Are you using tap water?

Are you doing a lot of water changes?

Both of those can mess up the depletion rates of calcium relative to alkalinity as each of them can add or deplete these.

[DougSupreme]

Originally posted by Randy Holmes-Farley

Are you adding limewater now?

I have added Limewater twice. When I realized that my calcium was outpacing my Alk (which hovers around 6 DKH without supplementation) I stopped adding Limewater.

How old is the tank?

The tank is approximately 4 months old. I started with 25lbs of fully cured LR and about 80 lbs of aragocrete. THe only bio load is my snail population which numbers around 50, give or take. (increasing daily due to the oversexed Stomatellas) :)

There are a few other processes that deplete alkalinity, one of which is the nitrogen cycle proceeding to nitrate and stopping there. That can be significant during curing of live rock.

Are you using tap water?

No. I'm using RO/DI for both make-up water and for water changes.

Are you doing a lot of water changes?

No. If anything I'm not doing enough, but then I also don't have much bio load to foul up the water.

[Randy Holmes-Farley]

OK, then I suspect that you really are using both in the standard ratio, and limewater is a fine way to go. If the alk is still dropping with the limewater, then you likely aren't adding enough of both calcium and alkalinity.

FWIW, this is a common concern that folks have, that they are loosing alkalinity faster than calcium, but nearly always it is just an illusion based on the fact that seawater has a big reservoir of calcium and not much alkalinity.

[DougSupreme]

so dosing limewater won't increase my calcium above acceptable levels with normal usage? I'm just worried about raising my calcium so high that I will never get my alk to stay up around 10 DKH

[Randy Holmes-Farley]

Not very likely, no. The concern with calcium getting high is low alkalinity. If you are getting there with a balanced additive, that won't happen. High pH is the bigger concern overdosing limewater.

[DougSupreme]

I just realized why my alk is always so low. I don't currently have a topoff container. I have just been adding my topoff water directly from the RO/DI filter. I haerd that the water out of an RO/DI could have a pH as low as 6. That would probably deplete my Alk pretty fast huh?

[Randy Holmes-Farley]

Purified water, especially in contact with air (that has CO2 in it) can have a pH of 6 or even lower. It won't, however, reduce alkalinity. It can be confusing, but adding and removing CO2 can lower or raise pH, but it has zero effect on alkalinity.

[need4reef]

thanks for the infor Randy!

I am having the exact same thing happening in my 4 month old tank....

[pondfrog]

Great thread as I was just about to post a conern over my Alk going from 9.5 to 6.5 repeatitively with Calcium only going from 400 to 380 or so. I guess this is close to what Randy has said is an expected change and why I am constantly dosing Alk and not calcium.
Are there any possible sources of an Alk sink, though?
algae, sandbed.....?
Steve

[Randy Holmes-Farley]

About the only thing that is an alkalinity sink is the processing of ammonia to nitrate. So as nitrate is building up, alkalinity can be depleted. If nitrate is not rising, but is steady, then alkalinity is not depleted that way (unless it is only being steadied by water changes).

Of course, a water change with water of lower alkallinity will deplete alkalinity.

[need4reef]

you da man randy!

[Randy Holmes-Farley]

:thumbsup: