| iwanto, to get your pH down you will have to add a water softener or R.O. unit.
You talk about adding hyacinth to help your filtration. If you are not confident in you filter then you should concentrate on upgrading the filter rather than lowering the pH.
I agree that KH of 89 is probably OK if you do water changes. Adding the coral will not hurt, but you are unlikely to see any effect.
-s te |