Hi. I had 7 chinese algea eaters in my 55gal tank. in the last 3 days i've lost 3 of them. the other 4 seem to be lethargic. they are laying around and are sucked up to the glass behind the filters. I have had these Algea eaters since late december and they used to be pretty active. here lately they have been real lethargic like and they don't even seem to be eating. and now these 3 have died. water is good. no issues. all the other fish are doing well and thriving. any advice?