Underfiltration you would see cloudy water from ammonia spikes and bacterial blooms. If you're worried about it, try to add more biomedia. But it also sounds like carbon/chemipure/purigen will help pull DOCs as well.
Shrimp and other Seafoods are very oily and will cause the 'slick' on the top of the water. Not to mention Rays have an incredible bioload because of the way they derived from saltwater fish, so their osmoregulation system produces more waste. A skimmer might help, that was the first time I have seen it effective on a FW tank because it usually dosnt froth like a marine tank. Apparantly it has to be pretty dirty to do so..
An MFK user in the past had Rays and was feeding it Silversides and Smelt heavily, with a similiar water change schedule. He got a bad 'oil slick' on the top of his tank, and his ray started to float on the top of the tank and had some slight curling. Lots of extra water changes saved the ray, combined with a feeding cutback. 30 Shrimp 2x a DAY is an INCREDIBLE bio-load for Rays and Aros, especially depending on tank size. 40% daily sounds like what you should be doing. If your trying to powerfeed to grow your fish faster, it's also just as effective to change the water as often as possible for increased growth rate.
Shrimp and other Seafoods are very oily and will cause the 'slick' on the top of the water. Not to mention Rays have an incredible bioload because of the way they derived from saltwater fish, so their osmoregulation system produces more waste. A skimmer might help, that was the first time I have seen it effective on a FW tank because it usually dosnt froth like a marine tank. Apparantly it has to be pretty dirty to do so..
An MFK user in the past had Rays and was feeding it Silversides and Smelt heavily, with a similiar water change schedule. He got a bad 'oil slick' on the top of his tank, and his ray started to float on the top of the tank and had some slight curling. Lots of extra water changes saved the ray, combined with a feeding cutback. 30 Shrimp 2x a DAY is an INCREDIBLE bio-load for Rays and Aros, especially depending on tank size. 40% daily sounds like what you should be doing. If your trying to powerfeed to grow your fish faster, it's also just as effective to change the water as often as possible for increased growth rate.
