Also, there's some nano reef chillers / heat sinks on the market that you can install on the tank.
Like this one from MarineDepot -
CoolWorks Ice Probe with Power Supply (Saltwater Aquarium Supplies > Chillers > Micro )
Description
* Efficient: converts electricity directly into cooling power
* Reliable: the fan is the only moving part
* Easy to Install: one hole, one nut
* Safe low voltage operation
* Environmentally Friendly: no gasses or chemicals
* 1-year manufacturer`s warranty from purchase date
The IceProbe is the ideal cooling solution for small aquariums. This quiet, reliable, and efficient chiller uses advanced thermoelectric technology to directly covert electricity into cooling power.
With its threaded probe, nylon nut, and silicon washer, the IceProbe, can be easily bulkheaded through a 1.25" hole into siphon overflows, prefilters, sumps, or even directly into acrylic aquariums.
A single IceProbe can cool 10 gallons of water 6-8F below ambient air temperature in a standard aquarium. Multiple IceProbes can be used in a single aquarium to achieve higher temperature differentials.
The IceProbe provides continuous chilling power. A separate temperature controller must be used to turn the the device on or off at predetermined temperatures.
Weighing in at only 2 pounds, the IceProbeŽ is powered by a separate 12 volt D.C. power supply and draws less than 50 watts.
Something else to consider... not cheap at $105 + the cost of a controller to plug it into, but its a solution...
Kind regards