Hello! I'm new here and in a panic about my green tree frog.

I've had him for about three months now and just yesterday I noticed a black mark on his side. It looks like it's cut into his side, but there's no blood. He's eating actively, but I do notice him sitting in the mini "pond" of water in his vivairum every morning; it seems he's being doing that for about a week or so now. And he hasn't been climbing up very high to go to sleep for the past few weeks either. I will try to upload pictures later.

Does anyone know what this could be? I have another frog in the tank and I'm wondering if I should separate them.

Both frogs are aprox. two inches. They are in a 12x12x18 bioactive vivarium with UVB lighting, moss, temperature at roughly 78 degrees, humidity at 50-60% with spikes up to 99% in the morning when I spray. They also have a waterfall, driftwood, and no rocks or small substrate that could accidentally be eaten. I change there water about once a week or so due the tank being completely bio, however now I am wondering if this may be the cause of some sort of bacterial or fungal infection?

I will probably need to seek veterinary care but I'm not sure when I'll be able to schedule the appointment with my herp vet.