I am keeping an outdoor gar tank. Yet i don't want to use a cover to stop sunlight from going into the tank. And i read up gar and pleco cant mix. Any tips and ideas?
Reduced organics (via lots of water changes) in the tank will help significantly along with reduced lighting periods. In your case since your outside I would suggest overdoing it with a UV sterilizer for green water you will get from being outdoors. You can get large pond models for a pretty reasonable price.
also maybe running some phosphate remover along with uv filter. Algae scrubber is a good idea as well, just make sure to periodically remove some of the algae so as to get the nutrients out of your system before they are released back into it.
If your tank gets algae as fast as mines can, scrubbing will get tiring after a while. I would say your best bet would be a uv. Plants could work too, I'm pretty sure gars don't mind plants.
Gars should leave the plants alone. They will seriously appreciate the cover though. So will their eyes. Fish left outdoors with no cover tend to develop cataracts.