Need some info on stingray parasites

Hi forum, I recently got 4 more rays to go with the 2 i already had. These 4 were with the seller for atleast 3 months, where they were feed beefheart mix and frozen bloodworms.

On the first morning they were with me i saw some white poop. That got me worried. I would like to know a few things about parasites & stingrays.

1) Does White poop only means parasites ??

2) Is white poop the only symptom of parasites, or it goes with others like swelling or loss of appetite or laziness ?

3) Will the parasites spread to the other fish in the tank, namely arowana ? If yes then how fast??

4) What are the various methods of treating it ?

5) Are these methods same for all the fishes or just for rays.

Waiting eagerly for your replies.

Its a 5' X 3' X 2.5'

Anybody ??

ohh great help !!!!
maybe you could help me with some links that i could'nt find while searching or by just simply answering my queries.

I saw it the same night that i brought them home. Could have been from the older rays but i doubt that cause i was keeping an eye on there's and it seemed fine just 1 day before.

After i added the new rays i added another filter to the tank to catch all the poop, so did'nt see any poop after that. I will turn the filter off tonight and see in the morning whats the poop like.

Yes they all are eating fine and roaming and foraging around for food like the older rays. Thats why i wanted to know weather there are any other symptoms than white poop.

Thanks

They seem to be acting normal, i will keep an eye on the faeces also.