Considering the soaking i think its a pretty safe bet that there are mites. You don't always see them on the snake or in the water. Its just how it goes. The only and only occurrence of soaking with my boa was because of mites. The only occurrence with our BP was mites and when the hot side of his enclosure got too hot because the thermostat was dislodged. I would assume that anytime you see soaking there is a problem. Now.... here we go!

We placed a tub of warm water with enough water to submerge the entire body and a towel that sat about 1-2" below the surface of the water on a heating pad set to low checking the temp with a temp gun making sure the water temp was good. Once it appeared to be stable at around 80 we started our clean. First up - snake in the tub, lid on, brick or other heavy object. I would not advise soaking for more than 30 minutes.

Totally clean out the tank.

Wipe down inside and out and the stand.

Scrub the water bowl and other washable items with hot soapy water.

Wood, rocks, etc in the oven at 250 for at least 30 minutes. Be sure to check for potential smoking. We never had a problem.

PAM according to instructions. (I am going to add that spray to our arsenal.)

We also spray the paper towels in an x pattern.

Once the enclosure and paper towels are dry put everything back together, make sure your baked items are no longer hot. They cool rather quickly but I would rather have a furniture free enclosure than a too warm snake so I wait at least an hour before putting these items back.

Remove snake from the water and dry off. Treated with reptile relief. Put snake back if all cleaning is complete and dry. Hang out for awhile if not. We always ran our guys from mites. I kept a qtip handy and the reptile relief. If you apply it directly to the mite it was back out, you can get it on the qtip, then SQUISH IT!!!!

When I was spraying paper towels I also did enough for 2-3 more changes and stored these in a ziploc bag to change the "substrate" every three days.

We stayed on paper towels for a month. Ranjan was NOT thrilled with this idea but you can see the mites crawling on the paper. I knew what our mite source was because we fought them for weeks. Everything would appear clear, add substrate back to the tank and BAM!!! mites

Now, NEVER buy substrate form a store with reptiles! We always buy ours from the grocery store.