You don't really have much in the way of corals that will consume alot of alkalinity. Alk
is used when corals form their hard skeleton. It's also used when coralline algae grows, so that may be what's using it. If you are seeing a drop in alkalinity, you should also be seeing a drop in calcium and to a lesser extent magnesium. When corals grow their skeletons or coralline algae grows, they use a defined amount of alk
, calcium and magnesium in that process. For every aprox 2.7dKH of alk
"lost", you should also see a drop of about 18ppm calcium and 2 ppm
magnesium. Do you also test calcium and magnesium? Depending on how often you do water changes and which salt you use (some are very high in calcium) you may not notice the calcium dropping, but it is none the less.
Natural seawater is around 7dKH alkalinity. I keep mine between 8-9 dKH
. As long as you stay in the 7-10 dKH
range you are fine.