Not satisfied by not finishing my first project, I boldly go where I have gone before. This time I approach my other hobby of fish keeping with all the unbridled enthusiasm of the wandering electronics geek. I’m going to build a fish tank monitor!

This was all started by building a small tropical fish tank for my in-laws. This will be sited away from where I live, and rather than the hard landscaped gravel aquarium with plastic plants which it started as, I have suggested a more living aquarium with shrimp, snails, few fish and easy plants such as ‘Cuba’ and lilies. In addition a much more capable external Eheim canister filter will scrub the water well, and I am recommending little if no water changes as that works very well for my 120l fish tank.

But all this will happen a long distance away from here and I want to know how things are going remotely – hence the felt need for a monitoring station. While there are ones like the Seneye they do need a replaceable slide every month, and others like the Mindstream or Apex are truly expensive – plus they are built to control dosing or other schedules like lighting. I can do all of that using a cheap timer, and don’t need the expensive gear for what needs to be a simple tank.

Ideally I’d like to hook up a couple of sensors to a single-board computer such as an Odroid or Raspberry Pi, and connect to the local WiFi to transmit readings through to somewhere else – none of that worries me at all and using things like MQTT make it all very simple. Apparently for the Seneye you don’t even need the branded web server as you can use another server to do it – see here. But the sensors are the right pain as I’ll explain below. I’d like to be able to read:

• temperature probe – these are simple
• pH probe – much more complex and needs both calibration, and removing from the water due to fouling. I could use something like this to read the probe
• NH₃ as this affects the fish badly
• light levels – likely simple as well
• water levels – no water = bad! Conduction strip or
• … anything else I dream up.

I don’t need a display nor a GUI front-end as I am happiest when treating my SBCs as remote and headless – I find it tunes the mind to not trying everything and understanding how to recover remotely without a keyboard.