Hello there, looking for advice.
I set up my first aquarium, a 40L tank 45x30x30, up aqua z series led lights 7hours/day, shiruba canister filter, pressurized CO2 system with ADA Amazonia. Planted some rotala rotundifolia, dwarf hairgrass and hydro sp. japan - no fauna. At that time I knew that the soil will leak ammonia but didnt know the high ammonia could melt my plants. So shortly after I set it up, I went abroad for a month and hoping that when I come back everything will be nicely grown in and the tank is cycled. Got my mum to top up water and check if lights and filter are working.
But ofcourse, I came back to a tank covered in GSA and BGA - all the glass, hardscape and most plants. 80% of hairgrass and the hydro japan died, but the rotala was going strong. Mum reported that the algae started after day 10, and then quickly got out of hand. So I took out all the plants and hardscape, leaving only the aquasoil inside with filter running. Vacumed the dead plant matter and some of the algae infested soil, lightly cleaned the filter which was filled with rotting plant matter and rescaped the tank - I only kept the rotalas. One week in now, still no algae.
Before algae bloom

After algae bloom - this is 2 weeks in. By the 4th week it was 3x worst, quote mum - 'like a haunted house'.

Right after rescape

My question is..

1) Why the algae bloom? I had the idea that the z series was considered low light, and with 7hours/day it didn't seem to me like such a big algae bloom is possible. Do you think it is because the plants started to rot from the high ammonia, and with all the decaying plant matter, the algae bloomed? Thats what I think, that made me took out as much decaying plant matter from the aquarium as well as in the filter. Being a newbie at this, I doubt this is the only cause of the algae bloom and I am hoping maybe someone can point out something wrong with my set up before the algae comes back again.
1) Is my tank cycled? - can I add fish? tested the water this past week and nitrite 0ppm, but ammonia still around 0.25-0.5ppm. Should I wait for ammonia to go down to 0ppm or is this just a normal thing with the aquasoil leeching ammonia for a long long time.
Terima kasih sifu sifu sekalian.

what's the temperature like? algae boom may not because of high ammonia though...