i find that a number of things mentioned before works, Clean water, high temp also after doing a water change, put the water in at about 20C/70F and letting it raise up slowly using the heaters and then the water ending up at about 29C/84F, also i think changing decor, feeding variety's of food (earth worms, shrimp etc).
ive not tried the mealworms thing but i would have thought it would work.