Why did my alkalinity drop?

[Just John]

I have had my 13 gal tank since Jan/Feb. Over that time the alkalinity has slowly increased to 7.9-8.0. Ten days ago it was 7.9. I just measured twice with my Salifert test and it appears to have dropped to 6.7. Why would this happen and will having it this low cause immediate problems? pH has remained at 7.9 - 8.0 since the beginning. Soft corals only. No fish. The only thing that has changed is that I began dosing Nitrate a little over a month ago and a turbo snail may have died recently. I was also out of town for a week last month, so my corals did not get fed as usual.

Amm - 0
Ph - 8.0
nitrate - 15
Phos - .015
Alk - 6.7

 

[Randy Holmes-Farley Verified Community Expert]

Dosing nitrate will boost alkalinity, and if something like coralline algae is beginning to grow, that will begin to lower it.

The 6.7 dKH is OK, but I'd boost it back to 7 dKH with baking soda.

This calculator shows how much is needed:

Reef Chemistry Calculator

Most soft corals also use alk and calcium to make internal calcium carbonate spicules.

 

[Just John]

Should I bring it up slowly, or can I do it all at once?

 

[Randy Holmes-Farley Verified Community Expert]

Should I bring it up slowly, or can I do it all at once?

6.7 to 7 dKH can be all at once.

Dissolve the baking soda in some fresh water and add to a high flow area away from corals.

 

[Just John]

Thanks as always! My tank might have died some time ago without your posts. Should I bring it all the way back up to 8 over the next day or so?

 

[arking_mark]

Monitor you tank for Alk consumption. If you're finding a consistent rate of consumption, you can either start balanced (alk/Ca,) dosing or do water changes with high-parameter salt.

 

[arking_mark]

Thanks as always! My tank might have died some time ago without your posts. Should I bring it all the way back up to 8 over the next day or so?

Rule of thumb is 0.25dKH per dose and no more than 1dKH per day.

 

[Just John]

Monitor you tank for Alk consumption. If you're finding a consistent rate of consumption, you can either start balanced (alk/Ca,) dosing or do water changes with high-parameter salt.

I can't understand why this would suddenly start happening.

 

[Randy Holmes-Farley Verified Community Expert]

Should I bring it all the way back up to 8 over the next day or so?

7 dKH is fine, and so is 8 dKH.

You're welcome.

 

[arking_mark]

I can't understand why this would suddenly start happening.

You tank is roughly 7 months old...I'll bet your seeing coralline algae growth.

 

[Just John]

You tank is roughly 7 months old...I'll bet your seeing coralline algae growth.

I thought I would have. But not much, even though my parameters have been stable for months. By coincidence, I just scraped some off of a plug this morning to try to get it going.

 

[Randy Holmes-Farley Verified Community Expert]

Soft corals such as leathers also use calcium and alk.

What sort of soft corals do you have?

 

[Just John]

Soft corals such as leathers also use calcium and alk.

What sort of soft corals do you have?

A toadstool, 2 sinularia leathers, too many zoas, and a fair number of mushrooms.

 

[Randy Holmes-Farley Verified Community Expert]

A toadstool, 2 sinularia leathers, too many zoas, and a fair number of mushrooms.

The toadstool and leathers will use alk if they are growing.

 

[Just John]

The toadstool and leathers will use alk if they are growing.

The toadstool is not huge, maybe 3" wide, but it has been having a growth spurt lately. Same with the other two. Thanks!

 

[Randy Holmes-Farley Verified Community Expert]

The toadstool is not huge, maybe 3" wide, but it has been having a growth spurt lately. Same with the other two. Thanks!

You're welcome.

Happy reefing.