High Consumption of Alkalinity & Calcium in 375

[aquaticsbeyond]

I have a 375 gallon tank (~425 total volume) that has no coral in it (unfortunately), but is using ~250 ml of alk and ~250ml of calcium per day to stay around 8.4dkh and 440 calcium. If I stop dosing, the alkalinity and calcium will drop low ~6-7dkh and ~350 calcium in a few days, Magnesium is 1400, Phosophate is .012ppm (hanna checker) and nitrate is .75ppm (read sea pro). I run Biopellets and carbon. Any ideas why my tank is consuming so much alkalinity and calcium? I thought it could have been an electrical issue, so replaced heaters in the sump. Salt mix was Brightwell but recently switched to Fritz Pro. Thanks in advance!

 

[EmdeReef]

Do you have coralline algae growing?

 

[biophilia]

Do you have a lot of coralline in the tank? Does Mg deplete as well?

 

[aquaticsbeyond]

no noticeable coralline and mg is 1400 when I test. Tested 4 times this month to make sure it wasn't causing an imbalance.

 

[biophilia]

This is really bizarre! I've heard of cases where calcium carbonate can bind to some types of GFO, but not sure if you're using it. Otherwise, maybe there is some other species of calcareous algae present on the rock that you're not easily able to spot. Maybe @Randy Holmes-Farley will have an idea.

 

[aquaticsbeyond]

yeah it's been frustrating at times. This tank has been setup for about 2 years now. I tried getting my levels under control about a year ago and I ran into the same issue, so decided to keep fish only for awhile and do water changes. So here I am again trying to get my levels balanced (which they are but use a lot of two part). I recently did a 125 gallon water change (3 weeks ago) and plan on doing another 125 gallon water change. Only thing I haven't tested was the skimmer pump and return pumps (I run two). I can always try turning them off one at a time to see if that changes anything. It would be nice to hear from @Randy Holmes-Farley to get his input. Thanks guys