Why is my Alk declining?

PTXReef · Jul 16, 2020

Question: Why is my alkalinity declining while my other parameters are the same?
I do not dose anything (other than 0.75 mL selcon daily in Tang's food). I do biweekly ~22% water changes using Instant Ocean Sea Salt.

Last Water Change (7/4/2020) : 20 gallon WC in a ~90 gallon tank biweekly

Test Kit: API Master Test kit, Red Sea Multi Test Kit Foundation Pro

Parameters on 7/9/2020	Parameters on 7/15/2020
Salinity: 1.026 Temperature: 78 F pH: 8 Nitrite: 0 ppm Nitrate: 5 ppm Ammonia: 0 ppm Alk: 7 dKH Ca: 480 ppm Mg: 1560 ppm	Salinity: 1.026 Temperature: 78 F pH: 8 Nitrite: 0 ppm Nitrate: 5 ppm Ammonia: 0 ppm Alk: 5.6 dKH Ca: 480 ppm Mg: 1560 ppm

Corals in my tank that I think would mainly use those elements:
-Candy cane, 2 hammers, 1 torch, favia colony, 3 acans, 2 goniopora, a 1.5 inch maxima clam
The rest are mostly softies: mushrooms, xenia, toadstool, finger leather, kenya tree

I have a Reef Octopus Classic 2000 HOB protein skimmer,an AquaClear110 (with no carbon), and two pumps in the tank.

All of the corals are doing fine, I am the only one worrying that I can not keep a higher alkalinity.
Thank you in advance!

ss30 · Jul 16, 2020

Your corals are using it and your water changes are not enough to replenish what they have used.

Randy Holmes-Farley · Jul 16, 2020

The only other things that would decline with alk are calcium and magnesium, and with a 1.4 dKH alk drop, the matching 10 ppm calcium and 1 ppm magnesium declines are very hard/impossible to see with a hobby kit.

PTXReef · Jul 16, 2020

ss30 said:
Your corals are using it and your water changes are not enough to replenish what they have used.

Randy Holmes-Farley said:
The only other things that would decline with alk are calcium and magnesium, and with a 1.4 dKH alk drop, the matching 10 ppm calcium and 1 ppm magnesium declines are very hard/impossible to see with a hobby kit.

Any better test kits that you would recommend? To up the water changes or to dose?

ss30 · Jul 17, 2020

IMO dosing would be best, you can use Sodium Bicarbonate (baking soda) just make sure it's food safe. If you use google and search on how to raise DKH there will loads of results and there is bound to be a few on here aswell.

Randy Holmes-Farley · Jul 17, 2020

ss30 said:
IMO dosing would be best, you can use Sodium Bicarbonate (baking soda) just make sure it's food safe. If you use google and search on how to raise DKH there will loads of results and there is bound to be a few on here aswell.

lol

Yes, bound to be some people here who know what they are doing. lol