Please don't use chemicals for these issues. I'll try to explain.
First on the "clarifiers," these use chemicals to bind suspended particulate matter into larger particles that will then (supposedly) be trapped in the filter media more easily. Unfortunately, the chemicals also bind the gills of fish. Never use them.
High hardness (GH) is not likely to be the cause. And while I'm on this issue, as you have rift lake cichlids you want hard water. They are well suited to that, the term "liquid rock" is often used for the hardness of the water in the rift lakes. Leave that alone, the fish will be better off.
As for the water clarity, I also can't detect anything in the photo, but I realize that in "life" it may be quite different. Is this a recent development, or has there always been some particulate matter obvious in the tank? If the latter, it may be related to water flow. The filter flow might keep whatever it is from settling out. Just a thought.
I must say this is a beautiful aquascape for the cichlids. Very nice indeed. [I hope those rocks are siliconed together...I'd hate to see one dislodge and bring them crashing down