What's an ideal temperature?

[lister]

I have a 200 gallon tank with an oscar,red devil,severum,synspilum,texas,istlanum,ellioti,silver dollars & a clown loach,the temperature has been at 80f,but I'm thinking of lowering it to hopefully reduce aggression a little,get more oxygen in the water,and reduce feeding perhaps.
I have no interest in breeding and have no pairs,so that's not an issue.

What would be an ideal lower temperature for the fish that I have?

 

[duanes]

Mid 70s is fine, could be even a little lower for the Texas and istlantum, but not necessary.
Texan and istlantum are from bit more northern areas of Mexico than your others.

 

[Egon]

I like to vary the temps in my tank seasonally, more for cost savings than anything. I think its good for the fish too. I let my winter temps drop to 75 and my summer temps get as high as 87 sometimes.

Your fish will be fine at 75. Yes this will decrease food consumption and most likely aggression.

 

[lister]

I'll try 75 then.
I think it's time for new heaters too - when I pulled one out it was cracked to bits and I've been turning the other one down by 1c on it's adjuster for 4 days in a row but the temperature of the tank is still stuck at 80f.