Caulk

I would buy a small tube of aquarium safe sealant, DAP makes one as well as there should be a few aquarium mfg. brands.

First though check that any aquarium bubblers or filter outputs aren't forcing the water toward that corner and causing it to wick up the glass between the trim and dribble down the glass. It's much easier to tweak the water flow or even slightly lower the tank water level.

Deeda said:

I would buy a small tube of aquarium safe sealant, DAP makes one as well as there should be a few aquarium mfg. brands.

First though check that any aquarium bubblers or filter outputs aren't forcing the water toward that corner and causing it to wick up the glass between the trim and dribble down the glass. It's much easier to tweak the water flow or even slightly lower the tank water level.

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We used both of these steps to correct the exact same issue on one of our 75 gal. tanks. Might seal under the rim on the inside of the tank, if the tank is ever drained and empty for awhile.

Thanks Deeda, you nailed it with the filter output.

You are welcome!!

Sometimes it's even a bit of algae or crud that builds up under the trim that helps to wick water out of the tank. I've also had the wicking problem with cords from heaters if they get gunked up with crud.

When I get used tanks that need a reseal I also seal under the inside tank rim as BlueSunshine suggested.