I'm very worried about my albino bristlenose pleco!?

I have a 40 gal community tank with real plants and a piece of drift wood. And other decorations. I got 2 albino bristlenose plecos about 30 days ago. None of them have whiskers so does that mean there all female? And one in my 40 gal is huge! Like 3 times the size when I first bought it. But my other one has barely grew a few millimeters! I'm very worried that she isn't getting enough food! Every night I split a algea wafer in half and just drop both halves in the tank after the lights are of and all the fish are fed! It isn't where I put in when I wake up but I've seen my other fish eat them and my juli cories also! How can I make sure that the 2 especially the smaller on eat every day!??!?!?! I no they are nocturnal or watever but I guarentee they eat in the day cuz I always see them attached to the side of the tank going up and down eating. I just separated the smaller one just now and put a algea wafer in with it but idk if it's gunna eat it. Why is one so big and the other so little! The only other tank I could put the smaller one in is a 10 gal. But I don't no if I trust the water. If male and female guppies, and a female betta can live in a tank withou dying, does that mean the the pleco would survive!? There's plenty of algea in the 10 gal but I wouldn't want it to get sick or anything. So wat should I do?