Air flow is important because 1) need a constant supply of carbon dioxide (greenhouse gas) to produce sugars need for root growth. 2) reduce chances of fungal growth 3) maintain a more constant temperatures.

Ok how often would I need to lift up the fish tank to let air under? or do I elevate it permanantly?

thankyou for your help I should have been more specific.

Currently I am using some upturned fish tanks and plastic bags as mini green houses. They get plenty of filtered light but no direct sunlight. Nothing has struck yet but its only been a few weeks.

If I elevate the fish tanks to let air in, even very slightly, the moisture level is drastically reduced and I cant see any moisture stuck to the glass etc. If their is a gap where the moisture and gases can escape it will. Thats why I tried to make it airtight, and I lifted the tank up one a day for fresh air. Is this suitable?