I've been quiet for quite a while on here, but work is still underway.
I have been focusing on writing and rewriting the sketches for the monitor units; at the moment the units work using a Wemos D1 to monitor sensors and relays, display the data on a simple Web page and also serve the data on a json page.
This means the monitors can operate standalone (for home use or for single tank operation) but can also operate as part of a network of monitors via the Pi-powered hub.
I've written a nice little python function which is capable of scraping json data from the json pages. This means I can easily get hold of each monitor 's data for display on a single Web page, and can also be easily uploaded to anot iot site.
I will aim to post more regularly!