you can just turn your heaters down.
It's likely the climate in the area making the temperatures high. I doubt anyone would be here asking how to lower their tank's temperature if they had the heater set to make it too hot! Worth checking the setting though.
You can leave the heater in, leaving it plugged in or not. It won't turn on to raise your water's temperature unless the water is below the set temperature.
rugrat-those clip-on fans work well. I used them in Florida with my saltwater reef when temps got in the 80s in the water (they need to be in the 60s to low 70s). I had a 110 gallon then and used 4 fans to blow across the water's surface. I could drop the water 10 degrees doing that. I also converted my fish to an opposite schedule. Corals (like your plants) need some light or they will eventually die, so I only ran my lights at night, when the temperature was the lowest, so the lights wouldn't add to the heat problem. Just a thought...
Beware though, that the fans will increase your water's evaporation (that's how the heat is carried out of the tank). Just make sure you are doing your normal water changes, not JUST topping off. If the water is lowered in the week by say 10% and you normally do a 20% water change, take out 20% MORE water, then add back 30%. Do do otherwise will not dilute the toxins you are trying to remove during a water change. The evaporation will increase the concentration of the nitrates (hopefully you have no ammonia or nitrite, but would concentrate those too).
