algae. it eventually accumulates like in hoses and on things. it just added to the messed up sump momentum and required more maintenance to keep cleaned out
then the light itself corroded badly vs outside sump lamps of the same type
reverse cycle lighting: why do you do this? do you really know?
I had to think that through for myself too.
here's my thought when i considered doing that: so the bad algae in the DT is sleeping, using O2, releasing CO2. OK so what. minimal amounts of algae make minimal impact of the buffer reserve, and it is just CO2 which is stripped with decent water motion anyway. I want to hurt this algae the most i can. so why would i be oxygenating the water for them with a reverse lit fuge? and while the fuge is sleeping, why would i provide extra C02 to help the DT algae while the fuge is sleeping? AND why would i not want the fuge right in there at the same time as the DT algae competing for the nutrients?
anyway, i thought that reverse cycle would be of no benefit to my system.
i would go with 24hr(couple hr rest is cool for all plants actually but...) before i did the reverse cycle.
edit: just regarding complicated crammed sump setups. the maintenance wore me down after several years. that really sucked a lot of the fun out of it. granted i dont have a livingroom display which gives me more freedom to spread out, but after a while you just dont want to fool with it like at first.
FWIW, my sump is now a single tub. it contains skimmer, couple rocks with non-photos in return flow, and return pump on soft plumbing.
sump maintenance, as in replacing the entire tub once every 2 years-ish takes me <5 minutes after draining it to swap for a new tub just lifting and replacing 3 basic things. couple periodic siphonings in there when stuff is accumulating in the corners, and that's it. no further cleaning anything down there because nothing is really growing down there except featherworms etc. i can do this forever. maintenance is the hard part of going the long haul for me so i try to reduce the complexity of it.