Agree 100% with what Deborah says. If you are by chance overfeeding your fish, you may end up with an excess of MTS. They are nocturnal so won't be very visible during the day at all, unless you overfeed. I consider them to be helpful for the most part (they can be a bit of a pest, the babies getting into your filter intake, powerhead, etc.) and I have some in all my tanks, but they will not fix or even help the problem you are describing, unfortunately. They will leave your plants alone, will stir your substrate a bit, and they are neat looking - all good reasons to keep them - but those are about the only reasons! **
I'll bet dollars to donuts that you have a pleco. For "cleanup" right"? Hah! I put my bristlenose pleco in my 55 gallon tank with a large piece of driftwood and boy, am I sorry I did. (He was in a 29 gallon tank with an undergravel before...the brown gravel hid the poos much better than this bright shiny white sand does)
There are "wood chips" on the white sand every day, which I get out once a week during water change day, but that's about all. A powerful canister filter on one side of the tank and a Koralia powerhead on the other side will go a long way towards helping with this, but it will still be there to some extent. Thankfully, in my case, it's mostly just wood that he's digesting, so has no effect on water quality...just unsightly.
Bottom line, if you have problems with visible poo on your tanks, more than likely you have a pleco (or possibly goldfish) and there is nothing that will remove it except for a filter or elbow grease!
** P.S. Ok, one more reason: people buy MTS on eBay for inflated prices, and they are the easiest thing to breed you can imagine. I sold 50 of them with a plant (Java moss and Java fern) for well over $10...twice! A quick and easy sale.