Light and its intensity can be a very confusing phenomenon, it is very hard for us to determine it's intensity with how our eyes percieve it.
I experience this with one of my low tech tanks standing under a roof window. Thus it recieves a lot of natural light from above. Last year around march i had a significant BBA outbreak and switched off all artificila lights. And actualy was astonished how bright the tank was lit by the roof window, switching lights on and off didn't make a difference in how i percieved it. A few weeks after leaving the lights off, the BBA became less and when the fall arived in october it was gone and i switched the lights back on. Now we are mid april again, same story, BBA is comming even the snails are growing a beard and i switched off my lights again and the tank is only lit by daylight.
Still it is filtered day light the roofwindow is opague and even i do not see the difference the extra artificial lights is obviously to much and favors BBA. What baffles me a bit, is the pond like bath tub i have in the garden. It stands on a sunny spot on the terrase and gets full blast daylight and sunlight at sunny days. And i never ever have seen a strain of BBA in it.
I only have cluess to think about why and since algae and plants are same family and what makes them thrive is a combination of light, fertilization and temperature as far as we know.
If the trigger to cause BBA to thrive only would be light, than the pond should have it by now, but it doesn't. So their most be going on something else.. And i realy only have cluess. The outdoor pond is despite it has the most light off all it is relatively much colder than the indoor tanks.. That is one clue that could have an influence on BBA. The indoor tank has it with less light but it's a stable 22°C.
I don't believe it is realy co2 related only, because the pond doesn't get it and the low tech neither.. Both have the same water and both have the excact same Ph fluctuation during the light cycle. Co2 might be only playing a role if you additionaly put it in, but if you don't there still is a BBA trigger to cause it to thrive.
That leaves me with Ferts, light and temp.. Of which i think it's the later 2, light and temp.
But what the proper combination is beats me to the punch.. I have another low tech planted shrimp tank with only about a 1500 lumens led light at 60%, no ferts and a stable 25°C.. I throw in BBA infested plants and 6 weeks later they come out clean. That little tank is my prooven BBA exterminator.
My fertilized high tech tank with a stable 0.5 pH drop with co2 has over 10000 lumen led running at 60% - 40cm high above the tank and 23°C and it grows BBA, not thriving but some older leaves now and then show a little.
So that's 3 tanks 1 pond and each has it's differet BBA issue.. And i didn't got very much wiser tho.. But light and temperatur has my focus i think the culprit hides in these 2..
