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DIY water quality monitoring

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GeoffS:
I'm an avid veggie gardener and as I have a fair bit of space to play with, I've decided to dabble in aquaponics
As farmed  fish can go from healthy to dead in a very short time when things go wrong (and there are so many things that can go wrong!) monitoring of the pumps and the water quality are important. Solar power is also under consideration. Small scale so fish tanks will only be 1000 litres or so.

Things to monitor with respect to water quality are pH, dissolved oxygen and ammonia levels, nitrates and a few others I can't remember right now. pH is a simple one but I'd like to know if anyone has experience with DIY sensors to measure dissolved oxygen and ammonia. I know there are commercial devices to do this but not on my budget. I'll start with the chemical based kits for aquariums but I like the idea of just being able to look at a web page over my morning coffee to check the systems health.


Joules:
My experience with ph sensors has been they drift over time, need regular calibration and corrode over a relative short period.  This was in relation to designs used in spa's, the outcome at the time was it couldn't be done to a satisfactory standard that an end user could rely on a built in unit for the warranty life of the equipment.  So ph paper is still used, and the same applied to other sensors used for long term chemical monitoring unless the sensors cost more than the spa.

I do hope technology has moved on though. Will follow your progress, good luck.

SeanB:
Simplest would be a conductivity measure, as it tells the ions in the water and is simple to do. A turbidity cell ( either transmissive, reflective or both) will tell you about suspended solids. For oxygen you are going to have to bend over and buy a commercial sensor cell, as they are not really DIY items, they are basically an electrochemical cell made to fine tolerances. Easiest is to use a trickle tower ( which is very easy to DIY with a big piece of plastic drain pipe and a whole pile of plastic shapes like reject mouldings and a blower at the bottom or a catch tank and a spacer) to ensure oxygenation is good, and place this in a shaded place where it will not get hot. You might want 2 so you can strip and clean the one while keeping flow going.

Good design is a lot better than fancy monitoring, and as you will have a planted area to dispose of nitrates easily it will be better to have a bypass to let the water get filtered through the plants as fertiliser.

Joules:
Well you got me inquisitive...  I found this, i know its a comercial unit but I was very surprised at the size, cost and fact it does all the requested.

http://www.seneye.com/

   I have no idea how reliable the product is, but if it had been around many years back I would have had a go with one.

GeoffS:
You're right about the cost of some of the sensors for this stuff (I'll check out Senseye thoguth) The standard aquarium monitoring kits will do everything except dissolved O2 but plenty of aeration (air pump and air stones) will keep that under control. From what I've read, once things are stable monitoring is a once or twice a week affair.
I plan on raising rainbow trout which prefer clean water so they'll be plenty of filtering and a high flow rate which can also help with O2 levels.

The electronic side might be best if it's restricted to monitoring temperatures, pump operation and water flow. All pretty standard stuff.

There has to be a webcam though, I'm fed up with cats on the interwebs! %-B

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