Long story short, I now had one guppy in a 5 gallon tank. He looked less active about one week ago. Then about 2 days ago he stopped eating. Then he just laid around with zero energy although his gills were moving. Then yesterday he looked really bad and I saw him dragging himself along the tank ...

I bought a glass sump (intended for a fresh-water tank) 2nd hand that has clearly been put together at home. The construction looks great, but you can tell its homemade since the seal has "frayed edges" and is a little messy. There is some discoloration along some corner seals and under some of ...