You need to attack the algea at it's source. Don't shut it down. First, consider your fish load and cut down on feeding. Every other day to start. Just what they clean up in a few seconds. I read somewhere many years ago that they only need a piece of food about the size of their eyeball.
Next, put a phos filter of some type in your flow, whether the filter cartridge (if you use one) or sump if you have one.
Next, a question. How long since you change your PC bulbs. If over about 8 months, that may be the cause, or at least, some of it.
Next, there are snails who will clean up the sand quite a bit. What kind of cleanup crew do you have. If you don't think it's enough, add more.
Finally, without knowing your water params, do a 20% water change every 5 days.
If you can get your nitrates and phosphates down, the algea won't have anything to eat and will die off. It took a while for the conditions to be ripe for algea, ait will take a while to cure the problem. Be patient, it will be OK.