Okay...

Bottled spring water is fine.

The rocks...I'm not sure how clean they'd get with hot rinsing. Usually boiling for 30 minutes will kill any parasites or insects. Some people use a 5 % bleach solution to soak int and then rinse thoroughly, followed by another heavily dechlorinated rinse.

Okay, so within the week the color has changed...so that means one of a few things...stress from the move and adjusting to the new home which is very common, contamination from the decor, contamination from the tank.

The lighting...it is good for them to have a day/night schedule as they would in the wild. No specific lighting is required if your calcium supplement has vitamin D3 in it. Is there light in the room they're in from a lamp or ceiling light? Sometimes keeping a mild amount of light on vs. a super bright light in the first few weeks can lessen stress.

Earthworms and night crawlers can be purchased at the pet store or even Walmart, if you have one. They are stored in the refrigerator, so you may have to ask for them. Just be sure to ask that there are no dyes or scents added to them. When people but them for fishing there are sometimes chemicals added to them to attract the fish, which can be poisonous. Canada has the best night crawlers by the way. I get mine from Petsmart and they're nice and plump. I actually have to cut them to size for my smaller frogs. Kinda gross, but it works. If you have to cut yours, cut the pieces from the lighter end of the worm, not the dark/mouth end. They can seal off the cut and regenerate new ends, therefore live longer when cut from the back end. Just a tip. You are right, feeding outdoor worms and insects is not recommended due to possible parasites and possible fertilizer contamination.

Good deals on the tanks. Be sure to wash them out with either the bleach solution, regular rinse, and dechlorinating rinse, or with vinegar and a regular rinse, and a dechlorinated rinse or spring water rinse. It is imperative that you do the dechlorinating rinse after using bleach, even diluted, to be safe.

Petco, if you have one, is also having their $1 per gallon sale until January 19th. This means you can get a 55 us gallon tank for $55. I'm not sure if you have that there too.

If you can get a photo of the nose without stressing your frog more, please do, otherwise just keep a close eye on it. Though, if hurt or infected, it may need vet care.

Water temp is important to know. American bullfrogs can tolerate cool temps. They prefer spring and summer temps most though. I keep mine at about 75 degrees F, which is about 17.77'C. They can tolerate 10'C (50'F), but they'll be less active and may eat less. You can get an aquarium heater for under/between the rocks or an overhead lamp heater for on top of a metal screen lid. Be sure the aquarium heater is in the water before turning it on and be sure it is not hot to the touch from within the water. Mine is between gravel layers so he will not burn himself on it. You can get standard ones and adjustable ones that you can set the temp for.

They could change color due to breeding season, though its likely stress.

I think I got all of the questions/answers. If not, I'll add them on.

Have a good night. Time for me to close my eyes, but I'll be back on tomorrow.