Hi skeleton,
There are a couple of nuances here that you need to think about. BBA is the trickiest of all the algae types because it cannot be pummeled into submission. ferts have nothing to do with BBA so EI is completely irrelevant in this case and I see no reason whatsoever to adjust your dosing or to adjust your water changes. the bigger the water change the better. There is absolutely no such thing as too much water change....EVER...
Ordinarily, most CO2 related algae, like hair algae, can be beaten by simply adding more CO2, but BBA occurs due to instability of your CO2. This typically means that when the plants need lots of CO2 there is not a lot of it around and when they don't need a lot of CO2 there is lots of CO2 around.
So one of the ways to beat BBA is to carefully manage the timing of your CO2 application, so that when plants need a lot they get a lot and when they don't need a lot they don't get a lot. So first of all you need to understand, in that particular tank, just exactly how the CO2 is behaving. We need to know just exactly when there is a lot and when there is not a lot of CO2 in the tank. The only way to get a clue is to take direct pH readings of the tank water at various points in the day. A pH reading every hour, or better yet, every half hour from 2 hours prior to lights on until lights off. The dropchecker is too slow to be useful in this exercise and a pH meter is a handy tool to have.
Generally the CO2 profile in the tank should be something like this:
2 hours prior to lights on - pH at it's maximum daily value => Turn gas ON.
1 hour prior to lights on - ph drops 0.5 units below maximum daily value.
Lights on - pH is at it's lowest daily value, approximately 1 unit below maximum daily value.
1 hour after lights on - pH is slightly above lowest daily value.
The above is an ideal scenario but it's very difficult to achieve. Often, if you are able to drive the CO2 to nearly it's maximum value (pH near it's minimum value) by lights on, the injection rate will continue to drive the pH downwards so that the fish begin to suffer. Maximum CO2 (which causes minimum pH) is required at lights on. A few hours prior to lights OFF, the plants start to drop offline and they do not need as much CO2. Many tanks have trouble in that they do not reach their maximum CO2 until several hours after lights on, and this causes problems, both for plants and fish.
Apart from your CO2 timing you also need to review the distribution of your flow to ensure that you have an even and strong flow across the entire tank. It may help to daily dose liquid carbon products in the mornings to help with the CO2 availability at that time.
By the time you fix the BBA the diatoms will also have been fixed.
Cheers,
