Hi, guys!
I'm already reading this forum for a while and am really stunned about the quantity of good information I could already find here.
Unfortunately one question still remained unanswered.
I'm planning to build a completely automated hydroponics controller. I've already read a bunch of threads on that topic (including Billies hydroponics controller which is really a great read!) but most of these projects just took care of the pH or were just ideas and were not finished.
My interfaces are both from Atlas Scientific for pH and EC.
The thing is that it's really easy to find cheap pH probes on eBay. Even the better replacement probes for the big brands are affordable. I'm not sure if these are suited for constant use but will probably have to find out myself.
Finding a cheap EC probe or even information on EC probes is way harder. I've read a lot of DIY threads of people building their own probes. Many of them used DC which already shows that they've probably just tested it a few times and never had it running for months or even years. So I've googled a lot and am almost still where I've been at the beginning. I've noticed that there are a few different probes though.
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The lab probes
These look like pH probes and have different electrodes. Mostly titanium, graphite or platinum. Some of them are temperature corrected, some aren't. I'm not sure if they are really suited for constant measurements though. At least 50$/piece. -
The process probes
These have various looks. Some look like this and some loke like this.
Does anyone know the difference between these probes? Why do they look so different? How do they measure the solvents?
So I'd like to know where to get cheap and good probes. I think pH probes aren't a big deal but EC probes seem to be.
The first ray of hope gave me this site: http://www.nengshi.com/en/
I've found it somewhere here in some thread. I spoke to them and I'm not sure if they really know what I need and if it fits my needs. For instance I've asked them about a probe that can measure up to 2,500?s/cm at least and they've recommended the probe ASDH-1 to me and said it can measure up to 2,500?s/cm even though their site states 2,000?s/cm for it. Since I need a probe that can measure at least 2,500?s/cm or even 3,000?s/cm those for 2,000?s/cm are too low. 5,000?s/cm would be perfect but I couldn't find such probes. Besides these strange things their prices aren't really cheap compared to probes from eBay for example. They offered me ASDH-10 (Which isn't even on their site) for 79$/pc and ASPS2121 for 77$/pc.
This was my research so far. Is someone here that could enlight me? 
Regards,
Chris