Growbed construction

The growbeds are 1200l teampoly stock water troughs. They are about 2 metres in diameter and 400mm high.
These were chosen as similar to those used by Joel Malcolm. However I couldn't get a reasonable price for custom made steel troughs/tanks so I decided to buy poly ones. Poly will also not rust and is fairly easy to work with.
In retrospect I feel that round grow beds are not a good idea as they are hard to arrange in a limited space (I could only get 3 of the 4 I bought into the available space in the shed) and stands are complicated to build for a circular shape. AND it took 4 months for the manufacturer to complete the order!
The stands were complicated as the pictures show however they easily support the weight of gravel and water when full- estimated weight is probably over 2 tonnes per growbed when full.
I have put a layer of 19mm yellow tongue chipboard over the base then 25mm of polystyrene sheeting. I plan to also wrap the walls with polycell or aircell blanket material when we get closer to winter next year.
The stands were set on bricks so that they had a slight fall to the planned drain plug area and the drain holes cut unto the base. A normal laundry drain fitting was then screwed into place with a fair bit of silicon to ensure a waterproof join. Details will appear in the plumbing post.
The growbeds were then filled with gravel- Bungendore 10mm brown- selected for its smooth feel and average stone size of about 10mm. Really I just went to a sand and gravel place and handled all the potential media and selected one which felt comfortable to touch. Some people use blue metal but it felt to sharp to me.
Before the gravel went into the growbeds I had to decide if I should wash it. I did wash one cement mixer full but decided it would take too much water and also too much time. So unwashed it is. I thought that the flood and drain cycle would eventually wash out most of the silt etc. And it has although it took much longer than I expected. The system has been running now for just over 2 months and we can only now clearly see the fish on the bottom.
I feel that the silt and mud which is still visible in the growbeds will probably be good for the plants in the long term anyway so it was probably the right way to go. The only real problem was that I couldn't see the fish for the first couple of weeks and it is hard to know how they are going when they are not visible.