Hi geordie41, welcome to Pond Boss and congratulations on getting a BioPod.
First, I'm not sure what you started with. Did the start up kit include either eggs or pupae in addition to the larvae. There may some confusion about terminology. I don't usually refer to BSF larvae as maggots simply because most people have developed an aversion to the term because of housefly and blowfly maggots (larvae).
The seeding kits that I send out with my BioPod orders contain both eggs, the dark prepupal larvae, and/or pupae. If you seeded your BioPod with only immature larvae then it would make sense that the activity is slowing down as they mature. Keep in mind that you very well may have wild BSF visiting your BioPod and laying eggs. Have you checked the egg disc? The eggs look like this: BSF eggs in a BioPod egg disc
It will be easier for me to help you if you'll read my blog page that describes my seeding kit. You can find it here.
It's not necessary to have the excess liquid that most people get. The "tea" is a byproduct of the larvae processing high moisture foods like fruits and vegetables. BSF do best in humid environments and if it seems too dry just add a little more water. I think it would be better to add too much water than not enough. I would try gradually adding more water until you see some tea being produced and then you can always reduce the amount a little. Also it would be a good idea to produce some tea because the scent of it is a strong attractant to BSF females. I would paint some of it on the underside of the lid or on the egg disc. (It's always a good idea to wash your hands after handling the tea.) Of course once the colony is established you won't need to worry about attracting adults, it will happen naturally.
I think your summertime weather would be fine for the entire BSF cycle. I think you could corral them in a large greenhouse of screen enclosure, but it's certainly not necessary. BSF aren't the best fliers and they only have a few days to mate and lay eggs so I don't think they'll tend to wander too far off.
Let me know what you think after reading about my seeding kit instructions.
