Leathers need a lot of flow to slough off their surface frequently. I'd bet that's your problem. If you have sufficient rock to compensate for bioload, you'd be ahead to remove the additional filtration you get with the fluval and run with enough circulation to let the live rock manage your filtration. Then you don't end up with an end product of nitrates. I'd also remove all but about 1/2" of that crushed coral. It's just trapping detritus and threatening your alkalinity with it in there. A deep sand bed is one thing, but all deep crushed coral accomplishes is a nutrient sink that will eventually dump back into your water column. Definitely make sure you're thoroughly vacuuming the coral when you do water changes. How often are you doing water changes and how much of a volume when you do them?
Barbie
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