Sorry for the late reply to your post. What you have done is a big step in the right direction. But one thing I did pick up on in one of your earlier posts, is that you are relying on the Juwel Internal filter. Just my humble opinion, but that is contributing to all your problems. Every Juwel tank I've had in the past, the first thing I do is take out the fitted filters that come with them.I have recently drained down my tank (3 weeks ago), cleaned everything thoroughly, removed the gravel and discarded the plants.
I have now tried to rescape my tank and have added Tropica Aquarium soil, Dragon stone, purchased new plants and have cut down the nutrients / easycarbo I was using by 50%. The lighting period is set to 6 hours and all was fine for a week and a bit and now I have brown algae affecting both the hardscape and the plants and I am wondering whether this is normal.
I googled for resolutions and it suggested I was either not getting enough or conversely too much light or because I have started anew this is signs of the tank cycling ? I have spent a lot of money to try and get my tank looking reasonable but I'm concerned I am heading in the same direction as before
All the muck accumulating in it is sitting inside your aquarium which is why I think your NO3 is always high. Plus everytime you try to clean any part of it, all the crap is released into your tank.
You should consider a larger external canister filter, much more efficient and far easier to maintain.