Alk Mystery

[QuiGonJay]

A tale of two tanks (both not quite one year old):

1 28 Gallon - 1.026 sal, 10 nitrates, alk 9.2, striped blenny, watchman goby, some crabs, mushroom polyps, small leather, caribbean rose coral

45 Gallon - 1.026 sal, 20 nitrates, alk 6.9 to 7.0, ca 420, mg 1320-1360, 2 ocellaris clowns, 3 pajama cardinals, CUC, 2 gorgonians, kenya tree, a few small zoas, mushroom leather, mushroom polyps, caribbean rose coral, some oysters (hitchhikers), leather coral, 2 LPS frags - candy cane and duncan. This tank has a skimmer.

Up until about 4 months back, the 45 Gallon had been running 9.0 ish Alk but since then never higher than 7.4ish.

My question: why is the alk so different? I dose Seachem 2 part Reef Builder in the 45 Gallon to keep the calcium up and while calcium and magnesium are always fine, the Alk seems to always hover near the danger zone.

Both tanks follow the same water change regime - 2 weeks, RO top off, same water change source. Both use Purigen and Chemipure elite in the media baskets to help with nitrates (seperate issue I can't figure out - I feed sparingly every other day but still struggle).

Could it be due to growth on the LPS frags (both are growing well - Duncan has added 5 plus heads, the candy cane one)? I would think that would hit the calcium readings more.

I don't feel I can add much more of the Reef Builder without sending my MG/CA too high - or is that not a worry? Is there a way to target raising Alk only without screwing up the other two? Should I not worry about it too much? The tank seems to be doing OK but that ALK just seems low and it bothers me.

Thanks for any and all theories!

[Dkuhlmann]

You have more corals in the 45 using kalk. What salt do you use

[disc1]

Could it be due to growth on the LPS frags (both are growing well - Duncan has added 5 plus heads, the candy cane one)? I would think that would hit the calcium readings more.

For every 7ppm of calcium they pull out, they pull out 1dKH of alkalinity. This often creates the "alkalinity is dropping but calcium isn't" illusion since the small calcium drop isn't really noticeable with our regular test kits but the alkalinity drop is.

[Art13]

The dkh dropping faster than calc could be a result of the mixing salt used, it may have a higher calc rating the the dkh could be low enough that you could be adding enough calc to sustain the system but not alk. I would suggest getting rid of an all in one type bottle for calc, alk and mag and instead going with a separate dosing for each of the major 3. either that or supplemental dosing of alk would be needed.

[QuiGonJay]

Thanks for the info. I will look to try a supplemental alk dose and monitor levels until the existing two part bottles are gone then look into separate dosing. Amazing that two little frags could suck up so much alk. :)

[Art13]

If you have coralline algae that could also be sucking it up.

[QuiGonJay]

Yup, definately do. Always something to learn in this hobby . . .:)