I keep all my tanks at a nitrate level reading which tests between at most between 5-10 ppm or mg/L---if i can rely on these tests,i've used hagens and aquarium pharmaceticals chemical drop style tests--i haven't gone even to 10 ppm.What levels do you consider the high end for freshwater rays in your experiences--so far i've relied on low stocking levels of smaller fish with good filtration-biological and mechanical,minimal chemical (10 turns an hour of total filtration per tank) and water changes of 20-30% every two weeks.
Darren
Darren