I been thinking about this, surely he could use a peltier. I've used them in the past for many a wonderfull thing. Wire up a thermostat of some sort, the problem would be where to mounth the peltier, I dunno how well glass would take to a peltier, but you could allways run pipes over it. And i'm sure a powerfull enough peltier could cool your tank easilly. The wiring may be a problem but if you need help or a diagram PM me. And i sem to remember them being priced at around $20 could be wrong, i dont live in the states, the power suplly might be about as much.