Why is BBA growing on my diffuser?

It's been a long story, but I converted my low light/low tech 125 gallon to a low light mid tech tank. I did this as my ongoing battle with BBA. I had horrible BBA for a long time due to excessive water changes in an effort to keep down nitrates (large SA/CA cichlids). I got a 20 lb CO2 cylinder and am misting CO2 from either end of this 6 foot tank. Plant load is about medium, because that's all the cichlids will allow. Plants include watersprite (a few floating, but mainly planted large ones, jungle vals, corkscrew vals, Anubias, java fern and java moss. Lighting is T5's and T8's (Coralife and Perfecto) for a total of 144 watts.

I've been using Excel to systematically eradicate the BBA menace, with some measure of success, prior to adding pressurized CO2. However, ever since I added the CO2, the rest of the tank is great, but area where the CO2 mist is strongest (heaters, filter outlets) are the areas accumulatin MORE BBA. And yesterday I took down my Rhinox 2000 diffuser to clean off what I thought was brown algae, but found to be BBA! What's going on here? Why is the BBA preferentially attacking these areas and how can I stop it?

FWIW, my filters are an FX5 and an Eheim 2028, one on each end. The Fluval uses a dual outlet output and the Eheim I am using a spray bar. Both are pointed towards the center of the tank.

I can see the plants pearling even with the heavy water flow, so they are growing well (the watersprite and the Java Fern are actually out of control).

I change about 30% of the water once a week and dose with K2SO4 (no need for nitrates or phosphates, I do the water changes to reduce them) and add a tablespoon of Epsom salts and 30 ml of trace (from local hydroponics store).

 

Thanks Tom. I put 6 SAE's in there, but only 2 survived. I am afraid the others didn't make it.

When I test the water before water changes, I am getting nitrates = 40 ppm and phosphates = 4 - 10 ppm. Should I be not worrying about that and trying to get the measurements as low as possible? Are you suggesting that I do EI with this tank also? I can certainly go to larger changes 2x per week, but was worried about causing other problems, since the original BBA problem stemmed from excessive water changes with no CO2 source.

At this point, I just want to make sure I am not taking a step backwards. Thanks for your pointers, as always. So what you're saying is that it's normal to have some BBA always in the high flow/high CO2 areas? So I guess some Excel or H2O2 to kill the BBA once in a while is sufficient?

Oh, and for reference, the tank currently looks something like this:

 

I have not calibrated the kits. I guess I'll have to do that. However, I do use the kit in a variety of planted tanks and have tested our tap water, and everything else seems to jive. And if you see the stock in my tank you wouldn't think I'd be too low in nutrients.

2xchocolate cichlids (8")
1xRedtailed shak (4")
1xtexas cichlid (5")
4xsilver dollar (5 - 6")
1xGibbiceps (6")
2xBristlenose pleco (1.5")
4xCorys of various kinds (1-1.5") survivors from 20+
2xSAE (2")

I have been using both Excel and H2O2 to kill the BBA, but I haven't tried to do the full tank yet. My Texas always seems to have bizarre behaviour after I dose with Excel. BTW, I am not dosing the whole tank, but rather taking syringe fulls and injecting it into the problem areas with the filters turned off. The tank is actually pretty good now, but my concern was that it was really bad right on the spraybars and outlets and on the heaters which are in front of the high flow, and hence my post.

 

No, I don't use a drop checker. I've been looking into it. I saw that one of the members on plantedtank.net is selling them. I guess I should pull the trigger and get a couple for my tanks. Thanks for the reminder.

 

LOL....lucky I'm past puberty and don't need to clear my complexion. Maybe if it'll clear my arthritis. I've PM'd on the guy on plantedtank.net for a coupla drop checkers. Thanks for the tip.

 

Here's one set:

The Planted Tank Forum

However, the set I bought is this one, but I'm still awaiting delivery:

The Planted Tank Forum