Kalkwasser doesn't raise carbonate hardness. It does add a excellent source of calcium. The ph controls how much calcium is dissolved back out of the substrate, if it's aragonite. But that doesn't happen unless ph gets below 7 at which time you have other issues.
of 5 will nuke your LPS
, but you know that already. Start adding soda ash or properly prepared baking soda. This can be bought for pennies. Slowly, over a week. I suggest shooting for 9-10Kh. Monitor calcium as that may tend to drop as hardness increases. You need to also check to see that Mg
levels are about 1300. All three of these relate to each other. The proper Mg
levels decreased the "see saw" effect between calcium and carbonates.
But with a light coral load, you might consider increased water exchanges with a reef salt that's higher in hardness.
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