Someone said to just unplug the primary one how would that help?
No, stop listening to that person.
Is your CEL still flashing?
I'm not going to say anything really about fuel additives or bandaid fixes but...it sounds like you mixed 1 gallon of whatever you used with not nearly enough fuel. 1 gallon to 1/2 a tank can be a lot depending on the car.
1/2 a teggy tank is ~6.5 gallons...that additive is 14% of your tank...if your gauge was at 1/2 & it's anything like my teg it's actually at 5 gallons...or 17%...eeekkkkkkkkkkk!
1/2 a tank in my Tahoe is ~13 gallons...1/2 is actually darn near half so that would be a 7% mix. The 'add this to 1/2 a tank of fuel' is really a dumb measure for additives...especially strong ones.
Did this problem start after the seafoam or after the paint thinner or did you do the two simultaneously? I'm thinking that you could have either overdone the seafoam possibly damaging some valves or you seriously washed out the rings. Either way, misfire codes on all 4 cylinders is seriously bad.
You don't have an ECU problem...the additives didn't clog your catalytic converter (it's not how they clog), your o2 sensors probably should be checked if not replaced, & you need to start looking elsewhere.
Your mechanic checked compression...did he perform a leakdown test? That will help indicate a source to your problem (like a ring (bottom end) or valve (top end) issue)
Stop guessing & hunting...diagnose than repair...
Cameron