I see ur theory but I don't think keeping ur co2 on all night has anything to do with it ..plus its not safe for the fish . I also got the ramshorn snails but remove them every chance I get.. I've tried everything to keep this algae from growing but nothing works.
Mr. Fish, I'm pretty sure what you have is rhizoclonium algae. It can be green or brown. Tom Barr suggests that this kind of algae can be induced simply by adjustments to CO2.
Just for the record, I don't keep the CO2 on all night, but close to it, and because I am holding the level steady, it is not dangerous for the fish due to my high surface agitation. That may not work on every tank, but on a 6 gallon tank like mine, with high surface agitation, I'm off-gassing the CO2 quickly. Also, my plant mass isn't very dense, so the absorption rate of CO2 with lights -on VS lights-off is negligible. When I left the CO2 OFF
for 14 or more hours, my CO2 level dropped quickly. This caused a very wide swing in my CO2 levels every day, and algae began to manifest itself...specifically the same kind that you are experiencing. I may be able to begin injecting CO2 a couple of hours before lights on and achieve the same results, and that would probably be the better way to handle it, but the end result is nearly the same -- that is, to keep my CO2 levels nearly constant while the lights are on. I have never had my CO2 levels rise during the night, which would produce the potentially dangerous situation for the fish.
Here is the discussion I referenced, above. Maybe you can find a technique that will assist you in this discussion.