Well, adding a slug load of CO2 only once a week is bad, vs keeping the CO2 low all week long.
Likewise, allowing the CO2 to drop often or vary confuses the plant. Algae are able to respond faster for a number of reasons.
Yes, I'd add more Excel if you wish to do (more) water changes. You an still do them with the above routine, just perhaps once every 2-6 months is all.
I missed last swap meet, not much incentive to go just to give away weeds
If you want to do the Excel + weekly water changes, I'd just get CO2 gas(tyhe lower pH does not bother fish if it's from CO2 only, Rift fish like the salts, those will remain in the water).
If you want to use Excel, dose about 1.5x the recommendations.
Do enough water changes to remove the dirt, algae and muck only.
Consider some algae eaters.
Tropheus moorii ain't bad
You will need to do some more work and add more rooted plants.
I would suggest water sprite over coontail.
The water sprite has better access to atmospheric CO2 and looks better and is easier to sell and you can root it later.