my other tanks in the same room are much lower temperature (but have a larger surface area).
Could you use a heat exchanger between the problem tank and the other tanks?
All cooling devices can only pump heat from one place to another. All the electrical energy that you put into an air conditioning system, plus all the heat that it takes from the room, ends up in the outside part.
Also, most cooling devices are more efficient if the temperature difference is less. Often that is down to reducing the temperature of the hot part, by big heat sinks and huge fans. For example, a 5 kW aircon system will have nearly 1 square metre of radiator, with a big fan.
The same applies to Peltier cells, but they are less efficient, so more heat has to be got rid of. The aquarium cooler you linked to has a heatsink and fan on the hot side. If you have the modules on their own they will overheat very quickly at any power. You need a big heat sink and fan to keep them cold. They will pump about 50 W with the hot side at 25 deg C and the cold side 10 degrees colder. However, the input power is 80 - 90 W so you have to get rid of 130 - 140 W. If you let the hot side get up to 50 deg C, that increases the differential to the cold side to 35 deg C, and only 35 W of heat is pumped, and the input power increases slightly, so the same amount of power needs to be removed. That is obviously much easier if the hot side is 50 deg C, but you get less cooling.
Something like this
Aqua Chill - Iceberg POU Water Cooler specifications cools 11.5 litres per hour while using 75 W. Now 11.5 L takes about 11.5 * 1000 * 4.2 * 20 = 966000 J to cool by 20 deg C. (The 20 deg C change is an estimate on my part). That is 270 W of cooling, while using 73 W. I think that shows why Peltier cell aren't used so much.
You still haven't said why that tank is hotter than the others. Is the pump a submerged one? If so, a radiator on the pump outlet to cool the water from that could be very effective.