Testing water electronically

[Modelworks]

I have just set up a aquarium and I'm going with live plants and establishing the tank as close to natural as possible. One of the things required to do this is water testing and fairly often, at least every 3-4 days.

I already have my CO2 production going , bottle of sugar+yeast, and is working well producing a steady bubble of CO2 every 2-3 seconds, those yeast are some hungry critters

So I need to test for a couple items and right now have to use chemicals. I was hoping though that someone might know a way to do this electronically then I might be able to automate the whole thing with a microprocessor.

Things I need to test for:
Water hardness
Ph levels
Nitrite levels
O2 levels
CO2 levels

For the Ph I was thinking a simple ohm meter might work if I could figure out the ohms to Ph conversion . CO2 had me stumped for a bit without really expensive sensors until I was sitting here watching the tank. After enough CO2 got into the water I noticed that the water the filter was dumping back into the tank had a lot more bubbles created deeper down into the tank. I'm wondering if I couldn't make a device to siphon off water, churn it up with a small motor , exhaust any gases created out through a tube with some sort of plastic sphere that would move up and down and count the movements with a optical sensor.

Open to ideas !

 

[bobdole369]

I used to work at a place that did salt chlorine generators. The idea was that you dump a couple bags of salt in your swimming pool, and pipe the water through this thing that was like a capacitor in construction - they called it a "cell" - it was platinum coated plates. They stuck 28V at about 9A on these plates and it generated chlorine and sodium, which cleaned and disinfected, then recombined.

Part of that was to measure the pH and the salinity of the water. Salinity is simple, the testing was done with a pulse and current was measured, the "sensor" being a simple isolated probe (2 conductors separated, immersed in the water. The more current went across the probe, the more saline the solution).

pH was done with a very inexpensive (relatively speaking) probe somewhat similar to this one:

http://www.omega.com/pptst/PHTX014.html

It's almost $200 at retail, but since most industrial probes of this type are over $2000, thats a steal.

The only other water probe I know about is "ORP", which is difficult to explain. The idea behind it is that as water gets "dirty" or germy, it has the "potential" to be cleaned. The ORP number is essentially how much oxidizer or reducer needed to bring to zero. It doesn't necessarily mean that its clean all the way at that point.

I found a few other probes - nitrite and what not I've never seen electronic probes, but the CO2 and O2 are gonna run you a couple grand.

 

[Mark R]

Each of these can be measured using an 'selective electrode'. This is a specially constructed 2-part electrode, containing a membrane which is permeable to a specific ion. The electrode then generates a voltage proportional to the concentration of the ion.

A pH electrode, uses a glass membrane which is permeable to hydrogen ions. Similar electrodes are available for water hardness (calcium) and nitrite.

O2 and CO2 can be measured using a similar process - but require a small current as they work on an electrolysis process to generate the ions (and are more difficult to calibrate - as they must be calibrated with known concentrations of gas, so require a series of precision mixtures of gases).

A reasonable pH electrode should be available for around $100-200. They can be obtained with signal conditioning electronics or with an appropriate all-in-one data-logger (at a higher price).

Other selective electrodes are a more specialised, and would cost more (in particular, the nitrite electrodes are rather specialised).

 

[William Gaatjes]

I only can think of this...
At my work we (I am not really a part of this project) use sensors similar to these kind of sensors for a device to monitor certain toxic chemicals and/ or to keep a healthy living climate.

On a sidenote :
That is a good CO2 argument though... Step into a building with large amounts of CO2 gas inside it. You will feel the difference when compared with lower CO2 levels.

I do not know if it works, is it possible to measure the CO2 of the water outside the water ? I would think so when thinking of evaporation.

Here are some sensors.
http://www.futurlec.com/Gas_Sensors.shtml

 

[Paperdoc]

Bottom line is yes, there are electronic sensors (with supporting electronics) for each of these items you are interested in, and there most certainly are versions that can output digital information that could be interrogated or captured by a computer with data logging software. BUT the cost is likely to be very much higher than you want to pay! You have about 6 parameters to log, and each sensor system is going to be $200 to $1000, so rough-guess your system at $3000 for sensors, PLUS the data logger software (I did not add anything for the computer itself). Then you'll need materials for regular calibrations of each sensor system, and the time to do that work. None of this stuff is as simple as "Set it and forget it." For the average home aquarium keeper, such automation is not worth the cost, and saves very little time and effort.

 

[OUCaptain]

Here are some cheap pen type meters. I've read you can use the TDS meter to measure the hardness. Technically though, it's going to measure all the dissolved solids. It might get you close though.

TDS meter

PH meter

The PH meter is a cheap one so I can't vouch for it's accuracy but if you pick up some calibration fluid, you can at least know how much it's off.

Sorry, can't help ya any with the rest. Not cheaply anyway.

 

[Modelworks]

After looking over the options I can't see how to do anything but maybe ph and salinity cheaply. I could use chemicals to change the color of the water samples then use a color sensor to record the values, but that is a bit cumbersome to set up and really not worth the effort. I'll probably just stick with test strips for now.

 

[Leros]

You might find some information here.

http://reefcentral.com/forums/forumdisplay.php?f=145

Its a forum about building control systems for reef aquariums.