Do you have algae in your tank? The algae eaters will scrounge up some of the flake food that falls, but it would be better if you could supplement their diet. You can buy algae wafers that sink. I wouldn't add a whole tablet for 2 algae eaters, that's too much, maybe 1/4 of tablet every second day (for perspective, I use Nutrafin tablets, they are 1/2" diameter). Or, parboil a piece of zucchini (mine loves that!) - you have to get it to stay down, you can buy veggie clips.
I think with platies you should be fine. Most problems with CAE's occur on big slow moving fish like angel fish.