you can run your actincs longer you do need to mimic the suns effect. I would take the sand out and wate till it is all out and then replace it, but that is me. IF you give the old sand a extreemly good washing in boiling water it will kill any algae, you have to keep rinsing it till the water runs clear I'd do a 1/3 of a bucket at a time let it all dry out realy good you can even use a baking sheet and put it in the oven. just leave the house for an hour. It may get smelly but the sand will then be good to reuse, after the oven treatment rinse again and let dry. This method kills everything in the sand you will not have algae growing from your sand. Once you put sand back in your tank get a conch I have a slider he does a great job. I have seen many conches at other peoples places most I have seen just stay on the top they will stur the top layer. The silver slider will bury himself and move along and stur the whole 3inches of sand that is in there, wow he makes a difference. hermitcrabs and 1 tuxeedo urchin clean the rocks snails clean glass and the rest of the tank.

Bill