The way that connection was plumbed is not correct, and can not be tightening that connection.
The pipes are glued with PVC primer and glue. Silicone sealer is generally not used in pool plumbing, so this looks like a temporary stop leak.
The connection should have a Union (that allows adjustment) or male coupling at the filter connection - that fits over the top of the threads that you can tighten.
The solution is to cut the pipe are remove both pieces (the 45 and the connection to the filter). And insert a union into the line at a minimum to allow for removal and adjustment. Use a pool grade union and not one from the Home box stores.
You could also ID the brand of the filter and get the correct fitting to attach to the filter.
If you need help maybe a friend could help. Its an easy fix if you have the right parts.