Your 18,000 k bulb is too high on the light wavelength to really benefit your plants. So effectively, your tank is 15 watts on a 10 gallon, which is low light. Are all your plants melting, or just the aponogeton and vals?
Apono bulbs sometimes mysteriously die if they've been growing for a long time without a rest period where they can dry out. You might want to do some research on that.
Apono bulbs sometimes mysteriously die if they've been growing for a long time without a rest period where they can dry out. You might want to do some research on that.