Aaron,
Phosphates are at around 2 ppm. I think this is OK.
Rich, I have used reference solutions to calibrate all of my test kits. I work in a lab so I was able to make reference solutions and 4dKH solution for the drop checker. The BBA is growing in the high areas of circulation and alot less in areas of decreased circulation. I say modified because I am testing my levels right now until I get the amounts just right. The main problem started when I realized that I was only using half the dose of nitrates recommended by EI and started dosing full strength. This is why I have gone a little leaner, thusly the "modified EI dosing."
Does everyone agree with trimming of all leaves that have BBA? I would have to trim most of my ground cover plants and a lot of leaves on my nana petites and Polygonum Sao Paolo.
Hope I did not sound too pedantic there. Apologize if so. I'm no expert but have been doing loads or research on just this subject over the past 6-8 weeks in my own battle against BBA thus my suggestions.
Sounds like your tests and DC are in order. Not sure though that increasing those Nitrates are what directly caused it though. It's hard to tell what factor it might be. I will say though that unfortunately one of the KEY recommendations to get on top of and getting rid of BBA is the full elimination of as much of it as you can, and that does mean fully pruning or at least excel, H202 or diluted bleach dips of the plants. Even after I did a full huge rescape about 2 months ago and soaked in excel and H2O2 of all my ferns, anubias and large driftwood pieces (which had it like it was a fur coat) and the seemingly full elimination of it, it still stubbornly returned bit by bit. It required me to spend about 20-30 minutes every evening after work, for at least 10-14 days or so, trimming leaves that I saw it starting on, and spot treating with a syringe with H202 and/or Excel. I then finally dosed 5x recommended daily amount of Excel for 3 days in the tank. It melted a bit of my vals but the BBA that had started on my driftwood died off or just seemed to go into a state of arrest. I have not seen much if any BBA in about 10 days now, but as mentioned, GSA now is a small but seemingly constant issue. Mostly on older leaves and on the glass. I trim those leaves and scrape the glass every couple of days. All this was before I institued a full EI regime disregarding whatever my tests said about my Nitrates and Phosphates from the fish bioload, figuring even if I'm overdosing the 50% water changes will help ensure I do not have too much build-up. And now, since cutting my light down to 8 hours from 9-10 hours and raising the lights (T5 HO) from 1" over the water to about 4-5", it seems the GSA has slowed considerably. I'm told and I read that GSA is almost always due to low phosphates but I have quite a fish load and the phosphates on all tests I try show 4-5ppm but I have been dosing 2ml of Fleet 3x a week anyway to see if it helps. And of course 50% weekly water changes. I may, for a few weeks, do 2x a week 50% changes as I understand with higher fish load that can help get on top of algae too. Maybe you might try that too? But as I said almost all BBA threads recommend to remove all you can by trim or dip to even have any chance of it being controlled.
Lots of great articles on BBA control here:
http://www.barrreport.com/algae-control
Might check those out too.