The first important point is that you should never lower the humidity on a tropical boid that has an RI. Under standard conditions, for burmese, bloods, retics, etc., I try for an ambient humidity between 65% and 75% and a substrate gradient temp across the cage of from low 80's cool end to low 90's warm end. The problem is that this turns into more of a juggling act when you start raising temps to assist RI treatment, especially with low room humidity in the winter. Warm cage interiors rapidly drive humidity out into the low humidity room.
Here’s the main issue with temps and humidity. Because the amount of water vapor the air can hold increases rapidly with temperature, the relative humidity actually decreases with increasing temperature, unless the evaporation potential can be met. This means that unless the rate of evaporation can keep up with the demand for moisture brought on by the rising air temperature, there will be an increasing net loss in relative humidity. A water bowl has one of the slowest rates of evaporation of almost any setup, as the surface tension of the water inhibits rapid evaporation. Cages with temps in the 80’s range usually do not have huge problems with humidity. However, when raising cage temps into the 90’s, the rate of evaporation from a water bowl alone will never reach anywhere near its potential, and the humidity within the cage can easily drop below 50%. Frequent misting, wick system substrates, or evaporation dishes containing saturated cloth, paper towel, or aspen shavings have more rapid evaporation potentials and will produce much higher humidity levels than even a large water bowl alone.
I used to battle low humidity levels in the winter, especially with blood pythons. I really believe that as many winter RI episodes with boids are caused by low humidity, as are caused by low cage temps. Low humidity air dries the lung tissue of tropical boids and this damages the tissue making it more susceptible to bacterial infection. Also, you may be using the correct antibiotic, but if the humidity is too low, the effectiveness of the treatment will be compromised. When raising the temps for RI treatment, make sure to closely monitor the humidity and try to maintain the percentage in the 75% to 80% range when dealing with tropical boids. Sometimes, the appearance of initial RI symptoms are caused by lung irritation due to low humidity, and many times it can be resolved before progressing into an actual RI by raising the cage humidity. However, observe closely so the appropriate action can be taken if the problem progresses.
On another related and important issue, it is highly possible that your humidity was even lower than you thought. Lower price humidity gauges are notorious for being inaccurate and usually read low. Unless you are willing to spend 150 to 200 dollars for a NIST traceable hygrometer with a certificate, you can never be sure if yours is reading accurately. However, you can test your own quite easily to see if it is reading properly, and here is the procedure:
1. Place a teaspoon of salt in a bottle cap or small cup and dampen it with a few drops of water (without dissolving it) to make it the consistency of wet sand.
2. Carefully place the wet salt and the hygrometer inside a see-through container and close tightly. Don't allow any of the salt to directly contact the hygrometer. You can use a zip lock bag provided it seals good and you leave some air inside as well, or a plastic food storage container as long as it seals airtight.
3. Let it sit for at least 8 hours at room temperature and note the reading on the hygrometer without opening the container. It should read 75%, and the difference is how much your hygrometer is off.
4. If it does have an adjustment screw or other adjustment device, adjust to 75%, through a small hole made in the bag if necessary, and then check again using the above procedure.
I have an expensive certified dial hygrometer I purchased many years ago and have checked it periodically using this method, and it does appear to be a very accurate way to check humidity gauges.
Kelly