If you do a large water change and your nitrates don't drop then there are only two options. Either you have multiple bad test kits or your source water is bad (whether initially or by contamination from the jugs).
even though its "not supposed" to be causing this - you've got to start removing variables to narrow down the cause.
There is absolutely no reason to stop dosing Microbactor7 in fact stopping it could make it even worse. I'm assuming the few who have suggested you stop using it are familiar with the product? Mike if there is one thing I am sure of its that you should definitely continue to dose bacteria. More "good" bacteria is exactly what your tank needs right now to help breakdown whatever it is causing this. It is basically helping your biological filtration breakdown the nitrates. If you don't have enough "good" bacteria in your tank and you stop dosing Microbactor7 the NOx POx is going to do you no good. The NOx POx is basically carbon dosing which means your feeding the bacteria. If you don't have enough good bacteria to consume the carbon then you actually start feeding the bad bacteria. I think your headed in the right direction just may take some time is all.
There is absolutely no reason to stop dosing Microbactor7
I've never been to keen on anything that claims to have live bacteria while sitting on a shelf at a LFS. There are so many different types of bacteria that populate our aquariums, most are not suspended in the water column but live on the rocks, sand and glass. One of the best ways to get a good dose of bacteria is to seed from another well established tank using a piece of live rock or some established live sand.
That said, I don't see how dosing bacteria could hurt.
Pretty sure it's ammonia>nitrite>nitrate
Given this presence of appropriate bacteria without using any product to provide bacteria, what would be the benefit of adding additional bacteria?
On the ammonia issue, it is certainly possible for an appropriate bacteria source to speed the nitrogen cycle. But so can some live rock or sand. I personally wouldn't bother.
That's the idea for organic carbon dosing to feed bacteria to cope with higher N and P inputs than the tank can process out without it.. I keep over 40 fish in an sps dominant mixed reef system and feed over 2ozs of frozen food daily plus other foods with no nuisance algae of any note and no bacterial supplements; just vodka and vinegar dosing.The indigenous bacteria have managed nutrients nuisance algae and cyano very well for almost 3 years without adding any bottled strains.
I started with just vodka and did get some patchy cyano .When I switched part of the dose to vinegar the cyano abated. Early on I also tried small amounts of sugar with negative effects on some fleshy corals. It seems to me the amount of organic carbon you dose and the type matters;adding bacterial supplements doesn't,imo. Even a burst in bacterial growth by bacteria in the tank as you get by dosing live bacteria should occur by bolus dosing organic carbon .
I would just point out that bacteria can very rapidly multiply if they have available food. That's why people can get food poisoning. So whether they come naturally or from a bacterial additive, they should be able to expand in numbers as needed, no matter how much organic you add.