Originally Posted by Andy Sager
Because you didn't add for alkalinity, this helps explain why the drop. As I suggested, test your new saltwater for KH
. This will be a good indicator of what you have happening in the tank just from the rock and what's growing on it. Remember, you are diluting this value as well when you add the RO
water to it. KH
is not a "stable" value. It changes through usage. It lets PH fall when it's not present in higher amounts and helps maintain a high PH when it is. It works in a similar comparison to nitrates. High nitrates in a tank usually means a low PH as well. I'll even bet that if you check the KH
tomorrow, it will probably not be as high as you saw it after the water change.
Hope this helps
+1 Andy is right. The pH, kH
interact with one other. Without adding anything, kH
will go down gradually when topping off with ro
water having 6 dkH
. Due to the "balancing act" effect, pH will also be affected by kH
. While Mg
in your case is minimal without corals. Raising the pH with additive is a bad idea since it will further drop your kH
and at the same time shock your fish and most likely the cause of your fish dying when compounded with low kH
. You should adjust your alkalinity by adding pure baking soda to your top off water. It will stabilize your pH. Make sure you have enough water surface agitation instead of additive to raise pH. It will give comfort to your fish with more oxygen.