I do have a K1 set up on my 600 gallon but I run a separate pump at 900 gph through it (55 gallon Rubbermaid trash can 50L of knockoff K1) from my sump I run 2 jebao 12000lph pumps, and I have a poor mans ultima set up (21" Hayward pool sand filter stuffed full of ultimate 2 media) with 3k gph pumped through it so close to 10x turnover. If you are going to have stingrays I would recommend using K1 in your setup it can handle very large bio loads stingrays produce approximately 10x more waste than fish from what I've learned in the stingray section. If your like me I started with one ray and now on my way to owning 5 rays they are very addictive.
Here you go, Thomas. This is what I was hinting at, and Carlos is telling us a bag of Matrix won't keep up with Stingrays. I don't keep Rays, but I know that they eat a couple times a day, ALOT, and they put out LOTS of Ammonia after they eat.
So, in these Ray tanks, these guys get Ammonia spikes and it takes the bacteria bed a little while to metabolize the Ammonia. Like they can actually measure big ammonia spikes after feeding Rays in these tanks.
So, you'll need LOTS of surface area for bacteria to grow. I had thought that matrix would be enough, but Carlos says go with K1.
Another question here .... you DO understand that Rays take a LOT more care and feeding than fish, right? Big reason why I don't have any--I go out of town for a week on business, I can't feed Rays twice a day. but, my fish can go 3-5 days without eating no problem.