It is most likely a respiratory infection. The best thing to do is find a vet. They will probably give you a prescription of Baytril. In the mean time, provide an infrared heat light so the snake can "bask" at night; the extra heat should do it good. The ambient day time temp should be in the upper 80's and night time ambient temp in the high 70's to low 80's. The "hot spot" can approach 100. Normal humidity should be around 65-70%, however, until the infection has past, keep the humidity about 40-50% to help dry it out.
Here's a link to some basic husbandry as well.
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www.ReptAquatics.com
wsrosser@reptaquatics.com
