Raising the temperature will help the bacteria. They grow better at temperatures in the 70s. They are very slow growing at temperatures in the low 60s and under.
I would use heaters that are based on about 5 watts per gallon of tank water, and let them heat the water. It might take several hours to overnight. That is not too fast for the cycle bacteria.
I have no idea how long fish lice live off the host, or at what temperature. If the lice on the fish had a chance to reproduce there might be some thing waiting to attack the next fish that enters the tank.
I can see a few options:
Research even more, and see if you can find the answer.
Salt the tank very heavily (1 tablespoon per gallon) and kill whatever parasites might be hanging out there.
Other treatment (bleach) that will kill fish lice, but will also kill the cycle bacteria. Followed by thorough washing and the fishless cycle.
Add a few sacrificial fish to the tank and monitor them to see if they get any fish lice. I would choose some bottom fish so that if any lice spend any of their life cycle off the fish, this is where they would hang out.
Here is more info about fish parasites:http://edis.ifas.ufl.edu/fa041
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26 tanks, over 3000 liters of water to keep clean and fresh.
Happy fish keeping!