I had the same problem using tubs. I have ZooMed UTHs on mine, one on each end for warm and cool sides. The sides were perfect...but the ambient was in the mid 70's. I fixed that on my tubs by clipping/hanging lamps for day and night(on timers) about 8-12" above the tubs. The bulbs were only 25watt so as not to give off too much heat. It worked great!