Spock wrote: ""The living wall is currently at 3.5byo BP" could you explain this please, as if to an idiot (me)""
I was being silly - the only thing that is growing on my living wall at the moment is primordial slime (cyanobacteria), I'm hoping to grow some more recent plants(such as mosses, ferns and african violets) on there once it settles down. 3.5byo means 3.5 billion years, BP means before present in geologist speak.
He also asked ""Do you have temperature fluctuations on the tank water, over a fairly long period by any chance?""
I don't yet have any monitoring system set up, so I've been looking at a cheap alcohol thermometer dipped in the water to note the temperature, but certainly the temp goes up and down with the weather. For example, it had cooled to about 18C over the few days of cloudy, cold weather (when it snowed on wed) and it was about 24 yesterday afternoon (28C outside). Today it is forecast to be 36C so I'll check in the late afternoon. The temperature is regulated at the top end by the dewpoint in the greenhouse - if the dewpoint is low the water will evaporate until the dewpoint and the surface temperature are equal. This means that I can regulate the top temperature by venting more air.
I noticed the other day that water was condensing on the pipes running across the roof (which move water from one end of the tank to the other). If I could increase the surface area (like say, fixing my heat exchanger) then the water would similarly regulate the highest temperature that the air reached, particularly if the dewpoint exceeds the tank temperature (and water condensed back).
These two mechanisms mean that when I get computer control set up I'll be able to tune the hot temperature of the water and the hot temperature of the greenhouse air. For cold weather I've only got the option of moving heat out of the water, so I need to design the greenhouse to be as hot as possible (hence the clear roof and walls).
Despite it being 30C outside, the greenhouse only reached 24C, being cooler than our house. (This is existance proof that a greenhouse can be cooler than outside) The cooling power is provided by both evaporating water on the rockfact/living wall, but also by the thermal mass of the wootank water itself.