Water in the bucket. Pumps it up through the drain hole to the opposite side. The overflow/drain was a stub of pipe to maintain the water level of about 2 cm. A friend had made the tray on a CNC for some one time job and was throwing it away anyway. I hoped to avoid making a top lid but it was needed to keep everything in place. 

I tried different variations. The floating stones (I forgot the english name for them) was the stupiest idea since they would get under the pots. That experiment lasted only a day. 

The roots kept going brown and look unhappy, recover a little and then go brown-ish again. 

I used proper fertilizer, bought two 25 kg bags of it :-)

Last night after posting I got into thinking maybe I could have had an aquarium thermostatic heater in the reservoir, 300w or something. Maybe... 

Appreciate input, I didnt get much meaningful input while doing this. 

PS, dog is my sisters. I never had one myself. But I like them.