Check the temperature of your water. It should not exceed 80F. From where I see it, a 520 gph water pump does not go into a cloner, it's simply to big and will probably be the reason your water temps are too high.
I know, next you are going to say what size of pump do I need? I really can't give you an accurate size, because I don't know how big your cloner is, or how many nozzles or what size reservoir you have. My guess is you need about a 150-200 gph.
With a 520 gph pump you are cooking the water!

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