How long would it take you to get another tank? Check your local Craigslist and see if there are any 20 gals for sale, there's usually a few if you look and usually pretty cheap.
Also, how are you heating the tank and how are you measuring temps and humidity? If you can I would bump that ambient from 75 to at least 80 to be safe, those temps won't kill but that's a respiratory infection waiting to happen if you keep them that cool for extended periods. If you cant afford an emergency 20 gal I doubt you can afford an emergency trip to an exotic vet, so for now priority is to bump those temps and keep them up, and get that tank ASAP. You could even use a tub like a sterilite or rubber maid if you already have one or can't find a cheap tank. They're actually preferable to tanks imo.
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