You're going to love the ecotech coral glue
You can use it in or out of the water - even apply it under water
Only thing I've found is it won't stick to slimy plug or rock surfaces, so a quick scrub with a nail brush does the trick for me
They made a short
video I found helpful
I don't know if it makes a difference, but I keep it in the beer fridge
I put it on top of the T5 fixture before I use it. This makes it flow well, but not runny
Oh, try to cut the tip as small as you can as it's not cheap and is really easy to use too much
