db,
I am glad you did not misunderstand me, I certainly do not claim to have all of the answers. To be honest, I am not all that concerned with air temps in the greenhouse, if I can maintain water temp. Having said that, I think the water temp will have to swing some, but I think that can be kept to a temp. that will not be detrimental to the plants or fish. I am fairly convinced, if I can maintain water temp. in a growing range 65 to say 75 during the winter. Then even if the air temp falls, as long as it stays above freezing, the plants should do fine, because their root system will be in warm water. They are not growing at night anyway, just sitting and waiting for the sun to come back up. I would also be surprised if I was able to keep the water temp. I am shooting for, if the air temp fell very far. I am planning a fairly well insulated Chinese style greenhouse with both end walls well insulated and the north wall well insulated and planning a insulating kilt on a cable system on the inside of the ETFE roofing at night to hold in temp. I will also be insulating under the concrete slab around my DWR troughs and very well around my FT. I will be building it next month and i will post some pics when I do. My plans are for my fish tank to be partially down in the ground, not because I think that is better, but because of space, I do not want to build any more space than I have to which is not being used for grow beds.