Fluctuating Conductivity Probe - Do I go by average or peak?

[clsanchez77]

I just installed my PM2 about a month ago now and I calibrated it at the 2 week mark, give or take. Even though I calibrated it twice, it reads the 53.0 mS/cm solution at 52.7 mS/cm. Close enough for me. My observation is that in a given day, the conductivity bounces plus/minus 0.2 mS/cm.

So my question is if I am adjusting my tank salinity, should I aim for the average to be at 52.7 or the peak to be 52.7?

Regarding ATO, I dose my topoff at 4.5 liters spread across 48 - 30 minute increments. This works out to almost 0.1 liter per dose. My system volume is 416 liters (110 gallons). SO the 30 minute change due to evaporation and topoff should only be 0.02%, or 0.01 mS/cm.

Thanks

[zombie]

It honestly will make 0 difference to the tank whether you target average min or peak with that variability (most struggle to get it down below 0.5mS/cm variation due to the relationship between salinity and temperature).

Whatever you do, DO NOT try to control your ATO based on the salinity (with the exception of low conductivity cutoff usually 1ppt or 2mS/cm below normal tank minumum) you will eventually crash your tank with that approach. Use volume to control the ATO with floats or optical sensors.

You might be an engineer if...You have no life and can prove it mathematically.

[clsanchez77]

Whatever you do, DO NOT try to control your ATO based on the salinity (with the exception of low conductivity cutoff usually 1ppt or 2mS/cm below normal tank minumum) you will eventually crash your tank with that approach. Use volume to control the ATO with floats or optical sensors.

You might be an engineer if...You have no life and can prove it mathematically.

Thanks and no worries, that was NEVER my intent. I am doing some water changes tonight and was wonder if I should cut the salinity back a bit, that's all. I never did install my float switches, but I do a fixed daily volume of 4.5 liters per day. Has not failed me in a year. I plan to add high and low switches for notifications, but if a switch fails, I know it will get 4.5 liters. If the dosing pump (or EB4) fails in either position, the switches will notify me. If both parts fail at the same time, we we are all related to Murphy. The most correction I have had to make to this is to add a gallon of water after a week, or remove half a gallon of water after a week.

I can mathematically prove I am an engineer. Just work out Dilbert's Salary Law

[zombie]

Ok. Just wanted to make sure. You would be surprised how many people have tried conductivity based ATO and came to the forums after crashing their tank.

I have a thread on some failsafes for ATO using floats that could help you dial the volume as temp and humidity change the evaporation so you have no need to adjust by adding or removing water manually.

https://forum.neptunesystems.com/sho...-ATO-Failsafes

For your scenario since you have the evap rate dialed in pretty well, I would suggest an OSC based approach with the OSC set to add up to 5 gallons a day permissive on the normal level float value and notify on switch stuck CLOSED or OPEN after 12 hours or high switch closed.

You might be an engineer if...You have no life and can prove it mathematically.

[clsanchez77]

Ok. Just wanted to make sure. You would be surprised how many people have tried conductivity based ATO and came to the forums after crashing their tank.

I have a thread on some failsafes for ATO using floats that could help you dial the volume as temp and humidity change the evaporation so you have no need to adjust by adding or removing water manually.

https://forum.neptunesystems.com/sho...-ATO-Failsafes

For your scenario since you have the evap rate dialed in pretty well, I would suggest an OSC based approach with the OSC set to add up to 5 gallons a day permissive on the normal level float value and notify on switch stuck CLOSED or OPEN after 12 hours or high switch closed.

You might be an engineer if...You have no life and can prove it mathematically.

Thanks, I will take a look. I currently use the OSC statement now. I have a spreadsheet I use to calculate the OSC formula for 2 - BRS 50 ml/min pumps based on observed dosing rates. I enter how much total daily volume I need and then how much daily alkalinity I need (after testing and manual correction). From there I get a OSC statement for my kalkwasser reactor feed pump and my straight RO/DI feed pump (from reservoir).

My plan was to add 4 float switches. The highest and lowest would trigger alarms with the lowest shutting off my pump. The middle two would bracket my RO/DI OSC overrides and would issue a warning. I do like the idea of monitoring the time frame, but since I already have a known volume spread semi-hourly, I may tighten that notification up to only 30 minutes.

My other failsafes are my ATO container is only 10 gallons and I fill it manually on Sundays. (I may automate this one day with a DoW statement and I ran thermostat cable with the 1/4" line for a future relay and solenoid.) So if the pump fails open, I can only put in 10 gallons...over the course of 760 minutes! Salinity will drop 10%, my sump still won't overflow, and I'll piss some inverts off but no one dies and no tank crashes. If the pump fails off, it takes 3 days for my return to suck air - micro bubbles - and it's only a loss of 3.5 gallons. The return pump has an elbow turned down for this reason. And now I have conductive to observe too.

Btw, you have had a lot of helpful posts throughout. You've been very helpful without any direct interaction. Thanks!

[zombie]

And typo above. I meant 5 liters not gallons in my post above.

You might be an engineer if...You have no life and can prove it mathematically.

[clsanchez77]

I also see there is now a "When" command. This will simplify things a good bit. Thanks.

[jkriegs123]

Hello,
I recently purchased Apex and am finding wildly erratic salinity/conductivity readings that don't come close to matching what I get with my refractometer. Below is an example:
Capture.JPG
After initially calibrating on set up, as you can see, my Apex read extremely low conductivity. After I recalibrated it shot up to high end of acceptable. Then I moved the probe in the sump and it shot up further. Then I installed an Apex probe holder in same region and it dropped again to well below normal range. Ugh! The most frustrating thing is my refractometer (which has been calibrated) shows my salinity is right in the middle of the acceptable range. 1.025. Please help if you have any advice to help me resolve this issue. Thank you.

[zombie]

Hello,
I recently purchased Apex and am finding wildly erratic salinity/conductivity readings that don't come close to matching what I get with my refractometer. Below is an example:
Capture.JPG
After initially calibrating on set up, as you can see, my Apex read extremely low conductivity. After I recalibrated it shot up to high end of acceptable. Then I moved the probe in the sump and it shot up further. Then I installed an Apex probe holder in same region and it dropped again to well below normal range. Ugh! The most frustrating thing is my refractometer (which has been calibrated) shows my salinity is right in the middle of the acceptable range. 1.025. Please help if you have any advice to help me resolve this issue. Thank you.

Did you let the probe soak in your sump for a week to rehydrate? The measurements you are getting sound like you tried to calibrate it immediately after opening it.

You might be an engineer if...You have no life and can prove it mathematically.

[jkriegs123]

Did you let the probe soak in your sump for a week to rehydrate? The measurements you are getting sound like you tried to calibrate it immediately after opening it.

You might be an engineer if...You have no life and can prove it mathematically.

It was calibrated upon installation, so it wasn't sitting in the sump. But then I calibrated a second time after it had been sitting in the sump for more than a month, and then I got a much higher reading, which then shot up and then way down below acceptable range after I moved it to the apex holder (but it was still in the same region of sump).

[zombie]

Gotcha. Do you have a voltmeter? Might be a stray voltage issue.

Could also be the wire too close to another (it's not shielded and is very sensitive so it can get wonky readings if the cord is too close to another).

What does it read if you dip back in the calibration packet?

You might be an engineer if...You have no life and can prove it mathematically.

[clsanchez77]

Hello,
I recently purchased Apex and am finding wildly erratic salinity/conductivity readings that don't come close to matching what I get with my refractometer. Below is an example:
Capture.JPG
After initially calibrating on set up, as you can see, my Apex read extremely low conductivity. After I recalibrated it shot up to high end of acceptable. Then I moved the probe in the sump and it shot up further. Then I installed an Apex probe holder in same region and it dropped again to well below normal range. Ugh! The most frustrating thing is my refractometer (which has been calibrated) shows my salinity is right in the middle of the acceptable range. 1.025. Please help if you have any advice to help me resolve this issue. Thank you.

This appears to be a stray voltage issue to me as well. I ran into this issue when I installed a second conductivity probe for my kalkwasser reactor, my primary one zeroed out. The probes are very sensitive to electrical interference. I preplanned my cable routing so that all sensor cables would route separately from my electrical cables, but I think even having a bundle of sensor cables and switch cables is still too much. If find shutting off the system and restarting it resets the readings on the probes and I usually only need to do this when I actually mess with the probes, so not very often. A ground probe may help with this as well.