20g is out for sure. Didn't think it was possible but needed to make sure. I can't do a screen room or a connect to house cause of HOA. Thanks though.If you're serious about it either get a largemouth for the pond, or screen the whole thing in (so it's connected to your house if possible, if not use a greenhouse or something) and you might be able to heat if enough.
But, for the love of god, drop the 20L idea!
What's up mate