In a 20h I, personally, wouldn't put more than 2 red eyes in. But I like to give my frogs plenty of territory.
My plant shop also gets Cubans in from time to time and I have taken some in and found them homes. But be cautious if you do. Cuban tree frogs get large and are ravenous. The Cubans I had made my white's look like thumbnail darts lol
4 grey's in a 35 sounds a bit crowded, but I know you have had them in there a while, so they definitely adapted.
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