wow, didn't know that about florescent lights. I'm using the Aquasky LED light fixture, suspending at about 14" above the water level. It's been up for about two months now, so I didn't think it was a cause.
I'm really baffled by the death of my rassys too as I've heard they are pretty bullet proof. The seven that were left after the initial 4 were found outside the tank seemed just fine, look fine. Ditto with the three that were left, and now with the lone last survivor. He's trying to school with the danios. It's so sad... hope he hangs in there until I can get this issue resolved and add some of his mates back in.
It does seem very odd to me too that only the rasboras are being impacted by the issue (I'm positive the shrimp were only impacted by the increase in co2 today). The danios are doing fine through it all, as are the shrimp now that the co2 is off and the airstone is running.
I have purigen in the canister filter. I'm planning to open up the canister and do a cleaning tomorrow. Will see if it needs a recharge at that time.