You don't drop the temp on rays as they are tropical and should be kept around 78-82º F all year long. When doing water changes you can change the water on the lower spectrum and some say it helps stimulate breeding.
Both my tanks are in garage so I can keep them warmer but the amount of energy it would take to keep tanks a couple degrees warmer in winter is not worth it. I have had three successful breedings at 75 degrees.
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What does winter have to do with the temp when you are keeping rays in a house? My temperature does not fluctuate all year long. Winter or Summer and we have more of a winter then you guys do in the South. Even if a house is cooler the heaters would still keep it at 80 degrees unless you don't run enough wattage for the size of your tank.
For myself I could keep the temp at anything but overall for heating and cooling purposes of my house it's better to keep the whole system around 77. This summer the tank was at about 80-81 and the ac seemed to be fighting the fish tank heat that it puts out into the house. Also the lower the temp the less humidity is put out and during winter I get water build up on my windows because it's super cold out side and I have a dehumidifier but that thing can cost as much as all the pumps do to run so less is more. Also if allot of people are on a drip winter brings in super cold water through the pipes so your heaters would need to work harder and longer heating the system. I use a mix of hot and cold water so it's just getting a good mix and hopefully not using heaters at all. I just try to maintain the best cost vs temperature level for everything. So when I say I was at 80 during the summer I guess I'm more saying I'm ready to keep my whole system a little cooler so I'm doing so. My basement stays at 74ish from the tanks and my main house level can be 67 degrees. We like the basement in the winter.
I keep mine at 81 year round, but it looks like from everybody else's temps I could drop it a couple degrees to keep the heaters from working overtime.