You can always use a small fan and aim it to blow across the water surface! It will keep it cool for sure, but ya have to keep up with evaporation! I had to use a few computer fans when I had a reef years ago! Just used them on my sump and it worked great. Also I have used them on the back of my canopies too.
Yeah I also have a problem bringing down the temp in my acrylic tank so I've given up. The tank usually 82 in the summer. But on the bright side, on hot summer days the temp in my glass tank seems to rise really quickly while the acrylic tank is stable.
This tank is AMAZING! It TOTALLY looks like a scene from Tomb Raider or Indiana Jones! I think my favorite part is how the anubias roots grow down over the rocks and look like hanging vines. It's that little touch that really makes it look perfect I think.
When I can no more stir my soul to move, and life is but the ashes of a fire
When I can but remember that my heart once used to live and love, long and aspire
Oh, be thou then the first, the one thou art, be thou the calling, before all answering love
And in me wake hope, fear, boundless desire.
if you put some comp fans to blow across the surface and lift your outake to increase surface agitation, you can significantly increase evaporation, and that will cool the tank. i know my stagnant betta growout jars are normally 3-4 degrees below room temp, you could probably get 6-8 with good surface agitation and airflow.