just had another thought. if you are losing your siphon, try blocking off one of the 1'' drains, this will increase the flow through the other one and may suck out the bubbles.
bruce
i have that exact same setup and my temp runs about 3 deg. warmer than room temp. I dont have a glass top on mine. the lights are probably 5'' from the water.
bruce
do your siphon tubes have air in them. that is the only reason i can think of. maybe you have small bubbles building up in them and stoping the siphon. i have a homemade overflow with a 1'' drain and it is going around 200.
i will take the powerheads. send me an email how you want the money and we can figure out shipping. wont be home tomorrow until around 5 get back to you then. thanks
bruce.
boo@cableone.net
I used lemon juice and it worked fine. You have to use a needle and inject it into them though. I just did a few at a time and checked my ph, no change. i figured it was best to space it out over several days in case it does change ph.