What's depleting my Alk?

[Hooloovoo]

All of my corals are currently in a QT separate from my main display tank. I have continued to check the alkalinity of the display tank periodically because the corals will be added to it eventually, and I want to be sure I have my parameters set right.

What has really surprised me is the need to keep dosing alkalinity to maintain desired levels in the DT despite the absence of any stony corals. My Calcium seems to be falling as well, but more gradually. Alk seems to drop at a rate of about 0.25 dKH per week; while Ca is falling by about 2.7 ppm per week. What is the mechanism that would cause this? Is it expected?

Recently, I did add a CUC. I would assume that the snails would use up some of the Alk/Ca to build their shells, but the falling alkalinity thing was going on way before they were added.

Here are some details about my tank that may be pertinent:

Livestock:
2x Ocellaris Clowns
1x Purple Tang
CUC consisting of nassarius, nerite, and cerith snails + 1x Florida Fighting Conch

Tank: Red Sea Reefer 525 XL (DT: 108 G, Sump 31 G)
Rock: 80 lbs. fully cured Pukani dry rock
Substrate: Aragonite sand

Filtration: Skimz protein skimmer, GAC Reactor, refugium w/ chaetomorpha algae

Lighting:
3x Kessil A360WE Tuna Blue
2x Giesemann Razor T5 w/ 1x ATI Blue Plus and 1x ATI Coral Plus bulb each
Refugium lighting: 1x Kessil H380

Flow:
Vectra M1 Return Pump
2x Neptune WAV powerheads

Parameters:
Salinity: 33 ppt (Apex conductivity probe and calibrated refractometer)
Alkalinity: 5.99 dKH (Hanna Colorimeter)
Ca: 391 ppm (Hanna Colorimeter)
NO3: not detectable (Salifert)
PO4: 0 ppb (Hanna ULR Phosporous Colorimeter)
Temp: 80 F

Feeding:
1/2 cube frozen mysis per day
1/2 sheet dried green seaweed every other day

 

[Brew12]

All of my corals are currently in a QT separate from my main display tank. I have continued to check the alkalinity of the display tank periodically because the corals will be added to it eventually, and I want to be sure I have my parameters set right.

What has really surprised me is the need to keep dosing alkalinity to maintain desired levels in the DT despite the absence of any stony corals. My Calcium seems to be falling as well, but more gradually. Alk seems to drop at a rate of about 0.25 dKH per week; while Ca is falling by about 2.7 ppm per week. What is the mechanism that would cause this? Is it expected?

Recently, I did add a CUC. I would assume that the snails would use up some of the Alk/Ca to build their shells, but the falling alkalinity thing was going on way before they were added.

Here are some details about my tank that may be pertinent:

Livestock:
2x Ocellaris Clowns
1x Purple Tang
CUC consisting of nassarius, nerite, and cerith snails + 1x Florida Fighting Conch

Tank: Red Sea Reefer 525 XL (DT: 108 G, Sump 31 G)
Rock: 80 lbs. fully cured Pukani dry rock
Substrate: Aragonite sand

Filtration: Skimz protein skimmer, GAC Reactor, refugium w/ chaetomorpha algae

Lighting:
3x Kessil A360WE Tuna Blue
2x Giesemann Razor T5 w/ 1x ATI Blue Plus and 1x ATI Coral Plus bulb each
Refugium lighting: 1x Kessil H380

Flow:
Vectra M1 Return Pump
2x Neptune WAV powerheads

Parameters:
Salinity: 33 ppt (Apex conductivity probe and calibrated refractometer)
Alkalinity: 5.99 dKH (Hanna Colorimeter)
Ca: 391 ppm (Hanna Colorimeter)
NO3: not detectable (Salifert)
PO4: 0 ppb (Hanna ULR Phosporous Colorimeter)
Temp: 80 F

Feeding:
1/2 cube frozen mysis per day
1/2 sheet dried green seaweed every other day

That really isn't much in the way of Alk depletion. It may not even be outside of the accuracy of your test kit.

That said, coralline algae and other "stuff" growing in your tank can consume Alk. Some Alk is consumed in the formation of your NO3 which would then be exported via the chaeto in your fuge.

 

[Randy Holmes-Farley Verified Community Expert]

0.25 dKH per week is very low. Abiotic precipitation, coralline algae, and even snails and other creatures can easily produce much more demand than that. [emoji3]