Watch for slugs and other pests on plants, in pots, under trays, in corners and beneath benches. At least once a year, take all your plants out of your greenhouse and thoroughly clean the greenhouse, benches, shelves and walkways. Spray with a hose to remove surface dirt and debris. Use a soft cloth or sponge.
Clean glass admits more light and heat.
For stubborn spots of algae, spray with Physan 20 or household bleach and let it soak before rinsing.