What is Reddit's opinion of Milwaukee Instruments 716690 ph Controller?

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You'll need a co2 diffuser ($5-$10 on ebay - to ensure the big co2 bubbles are dissolved in the water as best as possible) and probably a drop checker ($10 on ebay - measures the amount of co2 in the water to avoid killing your fish or not enough co2). I recommend the 'atomizer' style diffusers over the ceramic disks since they break up the bubbles better but they are a bit pricier.

Eventually, you might want to get a pH probe setup (I recommend the Milwaukee controller for $120 http://www.amazon.com/Milwaukee-Instruments-MC122-pH-Controller/dp/B00I47XIX2/ref=sr_1_1?ie=UTF8&qid=1461704736&sr=8-1&keywords=milwaukee+ph+controller+122) but that's clearly out of budget and a "nice to have" not required. Also, there are much better diffusers called "reactors" that use a powerhead to thoroughly dissolve 99.99% of the co2 - but they require a canister filter and more money. Definitely not required for a 30 gallon setup.

Highly recommend the milwaukee ph controller to stop a solenoid on your co2 setup if the pH drops too low: http://www.amazon.com/Milwaukee-Instruments-MC122-pH-Controller/dp/B00I47XIX2/ref=sr_1_1?ie=UTF8&qid=1448564321&sr=8-1&keywords=milwaukee+ph+controller

However, this type of setup is assuming your kH remains constant -- which it doesn't. Hopefully the atlas-scientific co2 sensor with a microcontroller (arduino or TI Launchpad) will allow a true cutoff setting if things become dangerous. Still, a hard pH cutoff around 6.0 is likely to prevent the most common total disasters caused by CO2 setups.

Yes, I’m currently using these paired together. I have had the unit for a year now with not a single issue and calibrates fairly accurate (+/- .10) I would highly suggest them however they are pricey. Well worth it if automating an entire system 👍

Milwaukee Instruments MC122 pH Controller https://www.amazon.ca/dp/B00I47XIX2/ref=cm_sw_r_cp_api_i_FS116BCTF8ZQRKYDTN94

Milwaukee Instruments MP810 Dosing Pump for pH Controller, 110V https://www.amazon.ca/dp/B01N4IQW22/ref=cm_sw_r_cp_api_i_XDBPMMEM7SZ0ZK45D3HA

Sorry to hear it. Everyone who runs co2 should get a ph probe to meter it. I have this one: Milwaukee Instruments MC122 pH... https://www.amazon.com/dp/B00I47XIX2?ref=ppx_pop_mob_ap_share

MILWAUKEE'S Instruments 716690 ph Controller https://www.amazon.com/dp/B00I47XIX2/ref=cm_sw_r_cp_api_glt_fabc_956XKWWQHNYRBEK5TYCG

What is EC?

It's not very clear what the problem is. Step 1 in designing a solution is to be clear what the problem is being solved.

The idea of using the color of a pH indicator as the signal is cute. No need for pH, just measure the color, and add acid/base as neded to correct it. But then your solution would be colored, and maybe you don't want that.

pH controllers are well-known devices. Here is one at Amazon:

https://www.amazon.com/Milwaukee-716690-pH-Controller/dp/B00I47XIX2

Why is something like this not adequate?

I started one of my setups with a keg regulator and 5 pound tank. It works reasonably well, but I'll do things a bit different in the future. I got a 1/4" to 10-32 reducer for the output, attached an SMC AS1200 needle valve, added a 10-32 coupler, attached a 10-32 check valve, and then did a 10-32 hose barb. I added a solenoid inline and everything was good to go. This has been reliable and works well. I should've made things easier for myself and bought a 1/4" NPT fitting with hose barb for CO2 tubing, the solenoid, and a pH controller. The keg regulator that I currently have actually has decent control of flow rate through the regulator itself. A pH controller would bypass the need for a needle valve by injecting CO2 only when your aquarium loses CO2. This is the way I recommend going, but a pH controller can be sort of pricey.

If you don't consider yourself handy and don't want to spend time putting all of this together you could buy a simple post-body kit that comes with a needle valve and solenoid. The components the other poster listed are also necessary.