Those numbers are not bad for Marquette in a hot summer. It would have been nice to get the TA down another couple points, but I don't think you had that option.After destemming and crushing
Brix from refractometer = 23.9
I have had good luck with the MBR31 strain with pH above 3.2. You have probably gotten all the pH shift you are going to see from the skins, but I could be wrong. I think you will be fine. Use MLB nutrients if you are concerned.pH = 3.28
So my question is, should I leave it on the skins longer? the MLB I have says it will work down to pH of 3.1.
Some yeasts can coexist with an active MLF. I think 212 is one of those, but look it up to be sure. The Scotts Lab Fermentation Handbook is a good place to go for this info. I added MLB to a couple of my musts last year for the first time (frontenac and petite pearl). It worked fine. I was worried that pressing might interrupt things, but it did not. Disclaimer: not much of an expert on this topic (nor any of the others really)Should I press it before adding MLB?
It depends on the variety. Some of them get downy mildew late in the season, like La Crescent. You start running out of choices the closer you get to harvest. Captan isn't a great fungicide compared to the others, but it has a really short PHI and it does control Downy. Tight cluster varieties may need treatment for botrytis, but that needs to happen at bloom I think. If powdery mildew is a problem, try to time an application with an effective fungicide a few weeks out that satisfies the PHI. My marquette has not shown very many late season fungal problems.Should I have been applying any other fungicide up to before harvest?