let me start by saying have learned alot by reading the posts hear. Now on to my problem. My rubber lip pleco died today. Last night it seemed fined even this morning when i fed them, it seemed ok. now a couple of weeks ago i lost a cory cat same sorta thing as what happened with my pleco. ok now on to tank details. its a 20 gallon, running a tetra wisper ex20 filter (looking change this week), currently stocked with 5 guppies, 1 red tail shark, and 1 cory cat. the other fish seem to be ok and dont notice any change in behavoir. the water paramaters are amonia- 1-2 ppm, nitrites- 0 ppm, nitrate- 20 ppm, ph about 7.8, temp about 76 degree. i do a 2.5 gallon water change every sunday, i use tetraqua aquasafe to nutrilize the water. does anything seem off to anyone. im new to this tank been goin since march. not sure if it is something im doing.