Temperature swing

[masterswimmer]

Hey Russ
I think the original point was missed. My issue started when I shortened my lighting period.
What I've been doing is running my lights from 8 am until 5 pm. The system is a metal halide compact fluorescents ( 2 150w MH and 2 96w compact fluorescents ) this would keep the temp at 77 ish all through the nite. During the day the temp would get to 80 and the chiller would keep it there but with the lites on so long I've been getting nuisance algae on the glass and sand. Now that I've shortened my lighting time from noon to 5 the temp in the tank never gets to 80 during the day, which means my nite temp at its lowest is 72 ish.
With all that being said now I have the need for a heater.
I hope this explains my issue?
Thx
Bruce

Hey Bruce,
I follow you. The problem is relying on the heat generated by your lights is insufficient and inconsistent for stable temp control on a reef tank. Even if your photoperiod was longer and the heat climbed enough to keep your tank at 75-76 at night I would still recommend changing your heating program to what I stated above.

Russ