OK Mike, I just read the thread you referenced. This is definitely a CO2 related algae. That means you need to be careful because this is not related to inadequate nutrient dosing. In a non CO2 enriched tank it will help to delete your water changes as long as you have a goodly amount of plant mass. In a tank such as yours, the limiting factor is the very low levels of CO2 which may be 3 or 4 times lower that what we find in the enriched tanks. This is fine because the the plants use several mechanisms to adapt to the low CO2. They do this by becoming more efficient at collecting CO2 in a CO2 starved environment .
The one rule they follow though is that if the CO2 increases they will stop trying to adjust to a low CO2 environment because they must produce a lot of a very expensive enzyme in order to perform this "Low CO2 adaptation." It takes about 3 weeks of low CO2 to fully adapt. The new water that you are adding once a week is very high in CO2 compared to the level that is in the tank. When you add this water the CO2 level rises instantly and the rule is broken - the CO2 level has not been maintained. The plants immediately start trying to adapt to a high CO2 level because of the water you've just added. Of course, after a day or so the CO2 level drops again and the plants suffer, because they stopped producing the low CO2 enzyme as a result of your water change. AS a result the plants fail to consume CO2 and they waste time and energy starting to adapt to low levels, then starting to adapt to higher levels, then having to re-adjust to low levels. They never optimize their enzyme production and therefore do not feed properly. Their cell perish, rot and then this algae attacks.
It's entirely possible that if you start adding higher nutrient levels then you will merely feed
this type of algae and so this could make matters worse. So I'm not saying that the EI dosing will
cause algae, only that it will exacerbate the algae you have now because this algae is not related to nutrients. You must fix this particular cause, which is unstable CO2.
Fixing CO2 related algae in a non CO2 tank is particularly vexing because you cannot fix it by adding more CO2. In this case you must fix it by stabilizing the low CO2 levels that the plants are trying to adapt to. This is best done by NOT adding extra CO2. This will be tedious because you may need to perform blackouts. Shutting down one of the tubes will help as well. Stop doing water changes and you will be on your way to fixing this problem.
Hope this makes sense.
Cheers,