Join Date: Feb 2011
Location: Indianapolis, IN
Having one platy/tetra is probably what killed it. Platy's and Tetras are both schooling fish- they need 6+ in one tank. Being alone is probably what killed it.
But since you haven't tested the water, it's possible that ammonia killed it. Tetras aren't very hardy when it comes to ammonia, but in 10 gallons I don't think this was the issue.
Also, you really need to get a heater to keep the water at a stable temp. Bettas need temps of high 70's to low 80's. 78-82F is what is recommended. Lights only heat the top layer of the water.
Just because I don't type with candy and rainbows doesn't mean I'm being mean.
My opinions are based on research and experience. Ask for help!
Peep, King, Tidus, Mars, Styx.