66-73% isn’t a very big swing. Powdery mildew is most at risk when you have high humidity (generally above 60%) and a lack of airflow. I’ve had swings from 30%-60% and the plant takes it. Sure, it’s not ideal, but the plant will still grow.
The reason why a carpet is a concern is mostly due to not being able to clean up as efficiently. For example if you spill nutrient solution or soil then it will be a pain to clean up. If you are growing in a grow tent and it’s on a carpet, that’s fine.
Cannabis will grow under the conditions that are mentioned there. Pretty decent recommendations there. Although, different genetics can react differently depending on the environment so keep that in mind.
Wow the plants really exploded in growth! The water temperature you mention of 20°C is good. Your pH issues could be impacted from the H2O2 like you mention. With your water temp now being under control, you can probably stop the H2O2.
An excess of some elements can inhibit the uptake of others so it’s generally recommended to stick to the ratios shown on the feeding chart; reduce the dosage if you feel you need to. When I used Bloom Yellow Bottles 7 years ago, I believe I started with a half dose according to their feeding chart. I definitely recommended reaching out to their customer service if you have more questions on how to use their nutrients. They know better than anyone on this forum I’m sure.
