Alkalinity stuck low

[Naw042]

Hi,

I'm having trouble increasing alkalinity in my mixed reef tank and can't figure out what's going on. My pH has also been low with wide daily swings. Some things I've tried...

-Added Seachem carbonate to get the Alk up to about 7.5 dkh then added kalk to my ATO. I added enough kalk to cause my calcium levels to increase (eventually increased from 450 up to 500) but my alkalinity was still dropping on a daily basis and ended up well below 7.0.
-Added Seachem carbonate to get the Alk up to about 7.5 dkh then added carbonate to my ATO. I added enough (5mL per gal ATO) that my Alk was almost stable (dropping less than 0.1 per day), but my pH was still no good and I wanted higher dkh.
-Added Seachem carbonate to get the Alk up to about 8.5 dkh then also added MORE carbonate to ATO (7.5mL per gal ATO) to gradually get the Alk even higher and hopefully increase & stabilize pH. After adding more carbonate to ATO the alkalinity started falling fast again (~0.2 dkh per day).

I know you should dose calcium and alkalinity evenly, but when I tried Kalk it resulted in calcium increasing and alkalinity decreasing over time. I know there's something else going on, buy I don't know what it is or how to fix it.

Typical tank parameters:
Water volume: 80 gal
Calcium: 420 - 450
Magnesium: 1600
Temp: 79 - 82 F throughout the day
ORP: 400-415
Salinity: ~1.026
pH: 7.65 - 7.9 (low with large swings throughout the day)
Tank age: ~6 months
Livestock: mix of everything (soft, LPS, SPS, clams, etc.)
Salt mix: Reef crystals
Nitrogen: All at 0
ATO: Neptune ATK using ~1.25L per day RODI

 

[Randy Holmes-Farley Verified Community Expert]

the problem may just be your perception that a drop of 0.2 dKH is high. That’s super low, although I recognize you were also dosing.

Alk normally drops 0.5 to 2.5 dKH per day and it isn’t clear to me you are outside the norm.

Just dose ordinary baking soda to a final value of 7-8 dKH each day, and let’s see where that stabilizes after a few days.