I have a 25g lagoon aio, which really only holds 18g. I'm losing 1.5 alk every week, which I have been supplementing. Calcium, on the other hand, has relatively stayed the same around 460. I do 5g water changes every week. I have 1 acan, 1 nephthea leather, a candy cane and just got a fl ricordea mushroom this week. No fish, 1 cleaner shrimp, 2 hermits and about 8 assorted snails.