Start dosing to raise alk?

Spkarim · Dec 18, 2020

(Reposting from general discussion forum)

Hi, I’m wondering how to address low alk and possibly low nutrients.

I have a 1+ year old 40g SPS/LPS/clam tank with 2 clowns, cardinal, wrasse, and fire fish. Corals show slow growth but not thriving. It has a 20g sump with some mangroves, using ATO with kalk that I think is saturated. I stopped skimmer and GFO several weeks ago after seeing nutrients low. Water changes are about 20% every 3 weeks or so with IO reef crystals.

I test rarely but tonight was surprised to find alk low. All tests salifert except pH (api)

alk 5.7
Ca 450
pH 8.2
nitrates - undetectable
Phosphates - undetectable.
76 deg, 1.025

I am trying extra feeding to bring up nutrients, but do have algae in tank.

my next step is to try to bring up alk, probably by adding baking soda.

what do you think?

thanks

SPR1968 · Dec 18, 2020

Just increase the alkalinity with whatever your using to around 8-8.5dKH as a general guide

As far as nutrients, maybe increase fish numbers and/or feed more, but you want to keep phosphate very low at around 0.03 or less to avoid many issues. A good nitrate target is maybe around 5-10

Randy Holmes-Farley · Dec 18, 2020

Baking soda is a fine way to boost the alk.

To raise nutrients, I'd first try feeding more. It is easier than dosing, which is also a fine option.

blasterman · Dec 29, 2020

Yeah....get that alk up. I've seeing enough growth on SPS tips where it's going to be consumed faster than water changes. You're going to have lots of problems < 6 dKH. Water changes however should be able to handle calcium until you really have some growth.

Use grocery store baking soda and the online reef calculator. I'm going to take a shot in the dark and guesstimate that tank is eating about half teaspoon of alk / baking soda a day. Maybe more. Only way to know is to get dKH up to 8 or 9 and see where it drops over 24 hours.

Remember that alk consumption is not linear. Once alk starts getting below 7 it's consumption slows.

Seems counterintuitive but you really need to raise nitrate a bit.