Basically with a planted tank IMHO the only difference is the water will evaporate slower. And you may have higher temperatures also.
My Wife's 10g only needs 1/2g/week top off with a covered top.
My 10g inside tank is open top and evaporates about 1g per week.
my 20gl on the back porch with an egg crate top (open) and heated evaporates about 1 g every day or two.
All three tanks have no filters, no circulation, no water changes. and fish and plants thrive in all three.
Of course if you have fish that jump you need some kind of cover. For instance, when I had silver hatchetfish on the 20g, I had to keep an eye on them when I removed the egg crate. (and several times had to pick up a fish from the floor) But my open top tanks with guppies and platys were fine.
I have a 75g heavily planted Discus tank that I leave uncovered. Right now I have amazon swords shooting stuff out of the tank (no flowers though) and vals that make small white flowers. I do not like covers on a planted tank because splashes and calcium build up on the glass would diminish the light output. As long as you don't have fish that jump like killies, either way is fine.
It took me forever, but I finally uploaded a picture of the surface of my tank. I have a few floating plants to help with nitrate/phosphate removal, but those long stalks you see are coming from my amazon swords. Each sword is shooting 3-4 stalks out of the tank and each stock has about 4-5 new amazon swords!
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