On top of that, some of my plants had started rotting and died while I was gone. Most of the salvina natans was falling apart, and the bacopa lanigera was gone altogether. The water was brown, and very hot. I bought a thermometer, and apparently the thermostat didn't work correctly. It should have kept the temperature around 25°C, but instead it was about 30°C in there. I solved this problem by turning the thermostat down a bit. It does keep the temperature constant, but always warmer than it's supposed to be.
Without a lamp, I wouldn't be able to keep any plants, and I saw no way that I could keep a decent lamp in this hood. I went to the aquarium store to see if they had any solutions for me. They had 18W clip-on lights but they were €40, more than I had paid for my aquarium originally. It just seemed too much money to spend. After all this, I didn't feel like carrying on with the aquarium.
I removed all the water from my aquarium twice, because it was really a rotten mess. Most of the plants survived though, and all seems well for now.