how many pH probes?

[+Mitch]

I currently have a pH probe in my sump and for my CaRx. I was thinking of putting one in my DT/overflow too.

What's motivating me was that my Apex pH2 port failed recently, so CO2 continued to get injected into the CaRx dropping my effluent into the 5 range, which dropped my sump pH into the sub 7.5 range (normally 8.0). Without a pH probe in the DT/overflow, I'm not sure how much of an impact this had. Fortunately this happened when I had just returned from a long trip. I know I can put in some better fail-safes for the CaRx pH malfunctioning, but wanting to learn what others do.

TIA

[victoly]

I would say it depends on two things:

Thing 1: Are you housing livestock in your sump? If so, it makes more sense to have a redundant pH probe in sump.

Thing 2: as a corollary to thing 1, if your CaRx dumps into the influent side of the sump, passing OVER said livestock, it again makes sense to have a redundant pH probe.

Realistically, you are backing up a backup, to save the media in your CaRx, because your DT pH probe *should* catch a dangerous drop in pH. Seems like the economics don't support the cost of an extra pH probe + calibration vs the cost of an entire container of media.

[+Mitch]

I currently only have frags in the sump, so am not too concerned about these nor the CaRx media.

I have the CaRx effluent dumping at the same end as the overflow (beginning of the sump), and the sump pH probe is at the other end in the return chamber.

I was thinking that if the sump pH gets too low vs the DT that I would shut down the return.

[victoly]

i guess the real question here is, could your CaRx be tuned lower such that the solenoid isn't kicking on and off? I'm no expert on CaRxs by a long shot, but I would think that you could avoid some headache that way.

[+Mitch]

i have the CO2 needle valve dialed in for a very low bubble count (1 every 3-4 sec), but the CO2 solenoid is turned on/off based on the effluent pH reading. in the scenario above, it got stuck on due to the pH port failure. i'm adding some fail-safes in case the CaRx effluent pH measurement gets hosed again, irrespective if it's the port, the probe, or whatever else decides to fail.

[victoly]

i guess the bottom line is, if it helps you sleep better, it's worth it. You've got a lot of money invested in your livestock, you may as well take steps to protect it and give yourself peace of mind.

[mrshall1027]

You could set a pH controller to shut off your effluent pump if the pH in the tank/sump drops below a set point such as 7.8. It doesn't protect your media but would keep the pH in your tank/sump from dropping too low. I have this setup using my RKL

[victoly]

His apex has the capability, it just had a malfunction and stopped working.

[George Monnat Jr]

I have two pH probes. One is in the skimmer section of my sump which is where the ATO pumps in the kalkwasser. The other is in the DT which is where the vast majority of photosynthesis happens. Because of those two things, I like to have two sets of limits. I can quickly tell when there's a problem with the return pump, too (pH and temperature between the sump and DT diverge significantly).