Sorry if I missed it somewhere but did you add all 3 rays at once to this tank, or in a very short period of time? I would say that could have been part of the problem if that is correct. As well as the oxygen level. I would say your tank did not have the BB for the bioload you added and the salt, water perams and low oxygen added up to stressed rays. Glad to here they are doing better.
On the color blind thing. You could be reading those tests way off depending on your colorblindness. If you live with someone else (room mate, G friend?) I am sure you could get them to take a look at them with you so you can see if you are reading them correctly until you get a digital, if you go that route. Or at least get a friend over to look at the tests with you once so you can see if you are reading them correctly. Either way, you really need a way to test accurately so you can keep an eye on the water, as it could throw spikes again if your bio-load is playing catch-up.
As far as behavior, remember the rays have not been in there new home very long and it can take several months sometimes to have a fish settle in and get comfortable. So you may see allot of new things in the future. Best thing to do is ask people on here (like you did), use common sense, and just make sure your water is were it should be. Definitely keep the bubbles going 24/7, for oxygen and entertainment for the rays.
Remember to be honest with people here (not to say you were not, just a reminder) so they can give the best advise possible. I think some people tell people they do certain things, like test regularly and do water changes weekly and actually do not. It is hard to help if the person helping is not getting the facts. You may get some rude comments from some members on your husbandry skills but you have a better chance of fixing the problem and saving your fish if the raw truth is provided. Once again I am not saying YOU were not being honest, this is just a reminder to anyone reading this that might need help in the future.
I just want to add my 2 cents on your filter setup. I know many here use canister filters and like them. I personally have never liked them as far as maintenance or efficiency. I am a big fan of the home built bio-tower type wet/dry filters with a sump, for fresh or salt water. The way I build mine, they are very easy to maintenance (and cheap) and do a superb job of biological filtration and they oxygenate the water very well at the same time, which is a big reason why they are so efficient. Not trying to push it on you, but if you are a DIY kind of person, I would look into it. I can show you one of my setups to give you an idea if you want. If oxygen levels are low to the bacteria, they can not do there job very well.