An alkalinity below 15 DKH
is fine but relative to the calcium level. Right now, based on the alk
level you have, the Ca
is too low. The easiest way to balance the two is by raising the calcium. Using the link I provided above, you should be able to find the right target zone. Exact numbers are not necessary, just be in the right range.
If you have been doing large water changes and it has not helped the ionic balance of the water, then the salt mix being used should be questioned and tested. If you have the same numbers as the tank water, then simpley adding a small amounts of liquid CaCl
will increase the level of Ca
and push down on the alk
. Add slowly and test each time to ensure you don't overdose the CaCl
and cause precipitation.
I would also suggest reading >>this
<< article in order to understand the relationships between these different elements and the many ways available to correct them.