Sean Dinh writes:

One thing great about TT is that the water get good oxygenation from flowing
down non submersed lava rocks. Do you suspend the screening horizontally as to
replace the lava rocks? Or are the screenings submersed? If the former, how many
layers do the water fall through before hitting the water level?

I use a spraybar in the one of the filter chambers. Doesn't take much pump
output, I think I have three 1/8" holes, pointed to get the water circulating
around.

I added it one hot summer when I noticed the fish distressed in the morning,
gasping at the surface. Solved it completely :-)

HTH