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I have rocks I boughtfrom menards kind of like lava rock but not as porous and I was just curious if sand would be better and if it would keep my tank clean longer? what would be the pros and cons of sand?

Its really a tie, both keep you tank clean the same amount of time. Possiably the rock just a bit worse since dirt can get trapped in it but dirt tend to stay on the top of sand. Sand looks better in my opinion and better with dirt like I said. Cons, gotta watch filter intake with sand getting into the filter.

I do have a pleco so would that help with keeping the sand cleaner?

The pleco won't keep it cleaner, but plecos do like sand as a substrate - I'd go with sand.