Recommendations are just that. Without a TDS meter, you will not know when you actually need to change out. TDS meter from
amazon is like 30$~ bucks.
Stability and knowledge is key.
Otherwise you are just guessing.
Noone can make proper diagnosis and help with bad information from API test kits.
Thats like asking a doc for advice with information provided by a friend of a friend.
No, you want him to get accurate tests from a lab and give a good diagnosis.
That applies here.
There are hobby grade test kits known to give as an insight into your tank then there is ICP tests to give you the numbers if you need to go even further details how your tank is doing.
As for the lights, you may get growth but color is probably to be desired. Not a resolution to the questioned issue but just saw that as a weak point.
Now, if I told you that I use hanna checkers, salifert or nyos for certain tests, a refractometer tested and calibrated.
You would get more definitive answers.
Even more when someone can provide ICP test data.
You can only get as much as you put in.
Some people can get away with water changes only but thats very few and far in between.
Success or success rate increases by taking good proven advice and applying it. What's unique about this hobby? It changes constantly and what may work well for one person will not always work for the next person.
So take each recommendation with a grain of salt. But as you see a pattern, hope it makes more sense.
Good luck finding the cause. I would start with the water agitation as it's pretty apparent.
Does fish go to the surface and create bubbles gasping for air? Does your overflow create some gas exchange or is it just flush with water line in display? Does your powerheads disturb the water surface? are you getting an "oil" slick on your water surface?
I had these issues on an AIO 20L so thats how I spotted the water surface issues in your pictures pretty quick.