@Nick, your pictures makes me worry about legionella decease that form in the cooling tower basins; please be careful handling & disposing of that slime. I suggest using an air filter at the suction side of you dehumidifier to eliminate particulate matters that help slime formation.
What I suggest during this COVID era is to try to buy a dehumidifier with pathogens killing UV bulbs; peace of mind that your home air is now pathogens free