Are you checking the temperature (83.7) with a thermometer or the heater setpoint? Make sure it's a thermometer and that it's accurate first of all to see where you really are.
Secondly, here's how the heat treatment really works. The elevated temperature causes the ich parasite to accelerate it's lifecycle - it doesn't actually cure anything. By accelerating the lifecycle, it like hitting the fast-forward button on nature. Once the ich reach the "free-swimming" phase of their life-cycle, because they are being accelerated they have basically less time to find a new host as they're swimming around before they die.
So, the warmer you go the faster this occurs. Having it only at 84 instead of 86 is a minor delta, so it may take a little while longer to get through, but it's not that much different overall.
Almost everyone who encounters ich and treats in this method will notice that when they start the treatment, things appear to get worse (in terms of "spots" on the fish) before they get better. This is normal and expected based on what I explained earlier about the acceleration of the lifecycle.
The important part of the heat treatment is to keep things warmed up for 2 weeks after all of the spots on the fish disappear. This is to ensure you've completely gotten rid of all the free-swimmers that you cannot see.
So, long story short, I would hold the course you're on and not reuse the meds at this point.
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