Well, here is where things get confusing and it's necessary to think clearly about cause and effect. Now, you were adding 5ml Excel daily but it seems you were focused on the algecidal properties of Excel instead of thinking about the reasons you had algae. What type of algae were you eliminating? Was it a CO2 related algae? If so then perhaps your minimum level of Excel should have been 5ml in the first place. It's best to think of Excel as CO2 first and as an algecide last, because when we focus on killing algae we will surely lose the plot. Reprogram yourself to focus on optimizing plant health so that if you have algae then your first train of thought ought to be "the plant is unhealthy". The type of algae that forms more or less tells you what type of affliction the plant has, and tells you why the plant is unhealthy. Therefore if you had a CO2 related algae this should lead you to the conclusion that the tank is poor in CO2. Adding Excel is thus used to improve the CO2, not to kill the algae.
I think this is where many people lose the plot. If you embark on an algae killing spree you're bound draw a lot of poor conclusions. Instead, try to think about going on a plant health spree. If you make the plants healthy the algae will subside to manageable levels or will disappear altogether. So 2 mls Excel+DIY CO2 is enough to keep some algae at bay with 27watts T5 over a 4 gallon tank but it is insufficient to prevent leggy growth. Personally, I would continue to increase the effective Excel/CO2 levels until I cured the leggy growth. The wisteria would have to be sacrificed if it could not deal with the extra Excel. There are plenty of stems out there that appreciate Excel so I wouldn't shed any tears over wisteria, that's for sure, because leggy growth indicates a far more serious dilemma, and, is a mission priority.
HOBs are not CO2 friendly and you may wish to consider replacing it with a small canister filter to achieve at least the 10X turnover rule (or more). This will improve flow and distribution while minimizing Co2 outgassing. Instead of spending money on sexy lighting I would prefer to spend it on sexy CO2 and sexy flow because one cannot use the first effectively without implementing the second and third. Air pumps also drive off CO2 so this makes it more difficult to bring the levels up to where they need to be at the most critical point in the plants diurnal cycle, the beginning of the photoperiod.
Apart from the ergonomics, or mechanical advantages of the new lighting fixtures, increasing the light energy input will only drive up the demand for more CO2, and if this demand is not met then the plants will be more likely to become unhealthy and will encourage more algal growth, so this is something to consider....
Cheers,