I have a set of 3 lens magnifying glass. The highest magnifying lens 20x. I can view something like for example a Cyclops very clearly. There are also magnifying phone apps.
@EggShappedFish I suggest sterilize aquariums with part bleach and water and rinse out. The traces of Chlorine from beach won't be a issue once dechlorinator is added to aquarium water.
@Stef I personally would replace the filter especially if it not running properly. If you decide to go with another Fluval AC 50 yes place a pre-filter on the intake. I would personally raise intake.
I definitely like @Guppysnail and @Tony s suggested I personally used Behr brand deck stain for a 180 gallon stand build. I don't have to worry about water and wood issues.