I often have a little current in my blackwater tanks but that is generally for the fishes and other inhabitants; the crypts certainly benefit a bit from a little water movement but don't need it. This tank has been "sitting" without pump nor heater for over a year...
Blackwater fish really feel at home in such a tank and I've been breeding species from genera like Betta, Parosphromenus, Boraras, Rasbora, etc. in such set-ups. No fish in this one yet since I'm waiting for Paedocypris. A low density of fish, shrimp, etc. helps to provide some nutrients; don't try snails though!
