The temperature of the water in an aquarium will be the same as the room temperature unless a heater or cooler is in the tank to raise or lower the temperature. This is one reason adding ice to the tank is dangerous, it causes fluctuations because the tank water will return to the room temperature as soon as the ice is gone. If the room is say 26C normally, the tank would not need a heater if the intended permanent temperature of the water is to be 26C. So, cooling the air in the room on a permanent basis will mean the temperature of the water in the tank will be the same.
Of course, it takes water longer than air to gain and lose heat, so the two temperatures will be slightly different if the air temperature begins to increase, or begins to cool, until they stabilize again. This is natural in the habitats, as days are warmer than the nights, though in the tropics this diurnal variation is not as great for the water as some try to make out. Water holds heat longer, and by the time it might begin to lower, it will be day again and the air temperature will increase as will the water. Sun striking the water will affect it (riase the temp) faster than just the air under shade.
Fish are stronger than people give them credit for. My bichirs tank managed to get up to 86. They are African fish, so it doesn’t matter too much. I turn all my heaters off in the summer. My tropical community tank got up to 83 and my outside tank up to 84. My patio ponds managed to get up to 87 - black pond liner in part shade most sun.
The light heats up my bichir tank, so I keep it off most of the day.