Standard purple PVC "glue" is not pvc glue, but is in fact a primer. PVC glue is clear. There are colored glues, orange and grey are typically CPVC and not necessary, blue or red is "HOT" glue for working with live systems that still have water in them. Oatey is the common home supply brand, the glue comes in a gold can. And no it won't harm the fish. It's the same stuff that your drinking water comes through.