I have never intended to brew that high before with brett but many a barrel of aging beer is subject to fluctuations throughout the seasons (only recently have some of the lambic breweries started climatizing their aging areas). I know higher temps are good for some of the fruitier esters from some of the belgian sacch. yeasts but I wonder about brett strains...
Has it formed a pellicle? Brett will often, but not always, form a powdery bubbled crust on the top to protect the culture from oxygen-loving competition. Its presence isn't an indicator of a good/bad pitch or strain but more a rough estimate of where the yeast is at and how much oxygen is in the headspace (or how much has been scrubbed for growth).
13 days is not long at all, my brett's sometimes calm themselves for weeks and then kick up intermittently. I assume the perceived inactivity is the culture adjusting its enzymes to tackle the next easiest fermentable available. I haven't gotten a 100% brett to arrive at bottle-safe gravity (1.000-1.006 is my target) in less than 8 weeks. I would recommend putting it somewhere it won't be moved as the pellicle is delicate and disappears with even a push.
How does the airlock smell after a bubble comes up? Bretts throw off my favorite aromas.
Is the brew in bucket or carboy? I don't recommending opening a bucket if it's in one. Just ride it out a couple months before tasting and testing.
How long did you let the starter go? I usually give all brett a two-step (first of 250 - 500 mL for 5-7 days) then up to 2L for a week before cold crashing and decoction (which takes longer as brett doesn't like to settle as fast as sacch). In case you are as obsessive as I am I'd recommend pouring off the clearest liquid off the top of the chilled starter. Then save the middle cloudy stuff in a sanitized jar in the fridge. Use the slurry on the bottom for the brew and the saved material is ready for the next starter in a few weeks.
http://www.brettanomycesproject.com...and-batch-culture-growth/propagation-results/
This shows the observed growth rates from an experiment.