A few issues were noticed during last weeks, though it was easy to fix those.
First issue was expected and was prevented before becoming a real problem - nutrient solution buckets need to be covered. The buckets have no lid and it was expected that some sort of lid will become necessary very soon to protect the solution from light, which could cause algae growth, and excessive water evaporation. Buckets are covered with "lids" made of foiled insulation and cardboard.
Using gauze as a mesh to prevent medium particles from getting into overflow tube was not a good idea, as gauze won't stay for long. It's made of cotton and being wet all the time it becomes a food for mold fungus, and finally falls apart. Gauze is now replaced with a piece of mosquito net. This thing is made of synthetic fiber and hopefully not edible even for fungus.
With lamps being so close to the medium the latter one gets dry very quickly, and it became worrying as the top layer of medium gets dry and warm, that could becomea problem for roots development. Besides that, humidity in the growbox is quite high, most likely for the same reason - water evaporating from medium increased by heat radiated from the lamps. So the medium is now covered with the same foiled insulation.