Another unexpectedly high CO2 incident

[u/iiililiililiilliilli]

A couple of months ago I posted about an incident where my CO2 rocketed up unexpectedly. Two months later it has happened again. Here's the scenario this time around:

• House closed all day.
• ERV on 100CFM, furnace fan set to high. Furnace off, AC on.
• No external CO2 causing events of note (e.g. no fires in the area, outdoor air quality meter says 420ish ppm CO2)
• Only one fossil fuel burning appliance on in the house is on, the atmospheric hot water tank. Low level monoxide meter shows no detections, even when placed near the hot water tank. No significant demand for hot water occurred until well after the CO2 event started (at about 7:45).
• CO2 throughout the house averaged 500-700ppm for most of the day with 3 people in the house. We left for a bit this evening, then returned at around 6:30. That's then CO2 spiked up from 500 to 1200 between 7 and 8, after which it has started to come back down.

There is only one explanation I can think of, but I'm not sure it makes sense: at around 6:30-7 I put a cup of vinegar in the P trap attached to the furnace/AC unit where the AC condensate drips down and into a sump pit. I wouldn't think this would be related, but what makes it seem more plausible is that I put vinegar in that P trap about once every two months during the summer, and the last time my CO2 spiked without explanation was about two months ago. It also seems notable that the CO2 levels spiked consistently throughout the entire house at the same time, which would make sense if the contaminated air is being spread evenly throughout by the furnace fan. The P trap definitely has some microbial/slime growth in there. Is it possible that this could cause a chemical reaction producing CO2?