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 the glass panels. Its yellow (or rusted color) and greenish/aqua in other areas. I have scrubbed the tank with water and salt and it remains discolored.
My concern is that I don't know how long the tank has been in operation and if these remnants are safe or not. Do I have to reseal the tank? I prefer to avoid that considering how difficult and fraught it is.