Temperature Problems

I have a 75 gallon subtropical community tank kept at 70 degrees Fahrenheit (~21C). It is no longer winter and cold in the house. The room temperature is up to 77 degrees and the tank is approaching 76. Even first thing in the morning after a cold night, the tank is still at 75 and increases throughout the day. The heater has been unplugged for a few days. I've been leaving the tank lid open to increase air exchange and vent out heat from the lights (wooden canopy). The stock is as follows:

8 Rosy barbs
8 zebra danios
8 Peppered cory cats
5 golden dojo loaches
5 platies

(Photo of 75 g is my avi).

Question is should I try to reduce the temperature or is a seasonal fluctuation okay for this stock? I foresee it reaching 78 as the summer approaches before A/C maintains 78 in the house. If I need to reduce the temperature, how?

 

I was having this same exact issue. My tank was running really warm 78-80 without a heater. Thankfully I was still cycling so I picked stocking that will work at this temp. Some suggestions that were given to me were more frequent water changes with slightly cooler water, floating ice cubes of dechlorinated water, an aquarium fan to blow across the water surface, and lastly the most expensive option an aquarium chiller.

 

My tank was set up in December, so heating was the issue, not cooling.

I guess the first part of my question remains: should I try to change the temperature or let it be?

I do 50% weekly water changes now.

 

Well 70 to 78 seems like a large swing to me but I can't really speak on stocking. Hopefully someone with more knowledge than I comes along.

 

Your fish will be fine. You're not keeping it at 78 year-round; it's just during the summer. I wouldn't worry about it.