Hiya
You're subscribing to ian_m's planted tank methodology rather than mine, so not that keen on sticking my oar in
I don't believe that the Juwel multilux LED need to be dimmed on this tank - the 50cm water column depth has already reduced substrate PAR to low to moderate levels
(look online at Tropica Inspiration page Juwel tanks, at professional aquascaper tanks (Jurijs mit JS, George Farmer, Filipe Oliveira ... with & without CO2) - sufficient light is an important aspect of leaf structure/health)
Algae is a component of planted tanks - it fares remarkably well in excessive light, moderate light, dim light - to me, limiting algae is about tank balance & maintenance rather than strongly limiting a single factor (eg, light)
What you're seeing is fairly typical - most aquarium plants are cultured emerse (think wet feet (fertilizer enriched), humid air, lots of light, CO2 ...), this gives them lots of stored energy for the transition to aquatic conditions (whatever they may be in an individual tank)
As plants establish, often first sign is root growth (why media such as Aquarium Soil with easily accessible (bioavailable) nutrients is helpful), followed by the development of new immerse (underwater) leaf structures - these are often thin & soft relative to emerse culture, also different shape
This new immerse leaf is now able to (readily) uptake water column nutrients, scavenge the low levels of CO2 & light
Some plants begin to adapt leaf structure almost immediately, other plants, more slowly
The breaking down (old emerse) leaf structure is a nice base for algae - some deeply attached into leaf structure (shrimp, snail etc crew will consume this algae while it's young/delectable/soft
), some just sitting atop leaf structure (easily rubbed off)
Of course algae will also try for new immerse leafs as well - a healthy new leaf tends to be more resistant to algae attack than the old emerse leafs - this is the aquarist job, supplying sufficient light, CO2, nutrients
Here again, I differ with ian_m, I'm a limited nutrient person - excess nutrient molecules can inhibit enzymes, block transport mechanisms, etc
Most natural waters that aquatic plants are sourced from are relatively nutrient scant (vs dense), so water column fertilizers should be sufficient rather than excessive
Daily water changes can help with minimizing algae (mechanical removal of "spores" at the least)
Physical removal of visible algae
Physical removal of plant breakdown materials
Soft brown algae that "rubs" off is usually diatoms - this is typical in tank startups, Otocinclus are the most effective diatom control
CO2 - gas - are you still planning this? I usually add this at the beginning to help establish plants, even if I'm intending to run non-CO2
enriched later, often tap water is a decent source of dissolved CO2 (relative to tap water that has been standing/water in tank) so again daily water changes can assist plant growth
Liquid Carbon - this can be utilized efficiently by some plants, less so by others; it has a definite algicide/algistat effect so it's often useful to add daily
You can also add carbonated water (look for low sodium) as a CO2 source - add daily; again this should be done with daily water changes to avoid buildup of other sparkling water components (most often sodium)
(Mick.Dk provided a dose somewhere)
Fertilizers - as you might guess, I prefer to add small daily amounts rather than dumping in a weekly dose (especially in a beginning tank)
What's your algae crew? How many?
Are you seeing new growth on the carpet (Monte Carlo?)? Other plants?