Well, it does get back to dose makes the poison, too much, kills the fish etc, too little does not kill the algae.
IME over the years, slow lower dosing worked best for algicides.
It took me about 2-3 months to kill the BBA in one large tank, but no issues.
Algaefix, H2O2 and Excel all bind to organic matter rapidly. Less than 1 hour I'd say in most any aquarium. Large water changes also add a lot of O2 for the fish respiration. Always a wise thing before any treatment.
I dosed Algaefix to knock back GDA with a single treatment with a single treatment of Excel, it did not eradicate a full bloom(90%). That also included a 60% water change and I also doubled the light for that week to see if increasing that would change the results. So it might have less/little to do with the chemicals.
The increase in light actually helped.
I noticed this before several years ago when I lived in Isla Vista CA.
Once the plants really took off from the added light, the GDA died back a lot and then a week or two later, nothing. Seems there might be a critical growth RATE to balance particular planted tanks. So plant growth momentum seems to play a role, how exactly, I'm not sure. I did not use chemicals back then at all.
Dark Cobra, I would keep using Clean tanks. Otherwise you introduce other variables. I noticed a big difference with ADA As vs the clean bare bottom tanks with the Algaefix. Mostly with moss infested with hair algae.
Easy to get since I have the moss outside and it's always got some hair algae available in the bonsai trays.
I suppose you could toss a lot of driftwood or some flith into a tank and load up, or use clay loam, ADA AS etc in one tank to see.
Seems that the more organically loaded tanks would have a higher requirement vs the clean tank in virtually all cases, the lower O2, or perhaps the dose killed the biofilter perhaps some. Those, not the chemical killed the fish/shrimp.