Apex Salinity probe keeps dropping?

[MarsReefer]

I am in the process of setting up my first tank and i'm having trouble with my apex salinity probe. The salinity probe itself is fairly old about 3 years old but it was never opened or used as I had my apex on a freshwater tank. I opened it up and calibrated it in my new tank and initially it seemed fine. It read 35 ppt and agreed with my refactometer.

However over the past 3 weeks it keeps dropping lower and lower and lower. I haven't done any water changes, just ATO as my tank gets established. Refractometer still reads 35 ppt. Below is what it looks like over a week, its currently down to about 23.

Any idea what is causing this or how to fix it?

 

[Lasse]

I have no experiences with Apex salinity probe but with GHL:s. When they do as this - is normally air bubbles that cause it. Test if it gets better if you take it up - clean it an put it back. If it this way - you need to place the electrode in the way that is a steady and fast flow over it. (and without bubbles)

Sincerely Lasse

 

[MichaelReefer]

I love my Apex, but, the Salinity meter isn't accurate at all. Mine goes all over the place all day.

 

[Been Caught Reefin]

Where is the probe? I had this exact issue and my probe was in my first chamber where the DT drain was and a skimmer. The tiniest bit of trapped air will mess with the reading. I moved my salinity probe to the return pump chamber where there are no bubbles and it has read steady ever since.

 

[ZombieEngineer]

I love my Apex, but, the Salinity meter isn't accurate at all. Mine goes all over the place all day.

This is because your temp compensation either isn't enabled or isn't set correct. The one in my mixing barrel needs 2.8 to stabilize. The one on my cube and mixed reef need 2.2 to stabilize.

 

[ZombieEngineer]

As mentioned by others, this could very likely be air bubbles. Make sure you have it in an area of your sump with minimal microbubbles. If that is not the case, the second most likely thing is if your temp increased or decreased over that same time period, your temp compensation could be disabled or incorrectly set.

Also, Neptune never likes to argue with me about this, but I have found that any new probe on one that was allowed to dry for a long time takes about a week to break in. My theory is that a biofilm develops that affects the reading and it takes a little bit of time for this to stabilize.

Also note: during the dry step don't let it sit for more than a couple minutes. I pull mine out of the tank, quick swish in RODI, pat dry with a paper towel, count to 30 and go next.

 

[MichaelReefer]

This is because your temp compensation either isn't enabled or isn't set correct. The one in my mixing barrel needs 2.8 to stabilize. The one on my cube and mixed reef need 2.2 to stabilize.

Temp Compensation?

I know its not air bubbles. Tried flipping it upside down, flicking it, etc etc.

 

[Vivid Creative Aquatics]

I would agree that is definitely not air bubbles - air bubble would cause a much more erratic and abruptly changing reading, and not likely to produce such a steady downward trend.

As others have suggested, most likely temperature related. @MarsReefer , can you post another chart but with Temperature overlaid?

Also - make sure to turn on and set the TC Factor - 2.0 to 2.6 is a good range to start with

 

[MichaelReefer]

I would agree that is definitely not air bubbles - air bubble would cause a much more erratic and abruptly changing reading, and not likely to produce such a steady downward trend.

As others have suggested, most likely temperature related. @MarsReefer , can you post another chart but with Temperature overlaid?

Also - make sure to turn on and set the TC Factor - 2.0 to 2.6 is a good range to start with

Didn't seem to change anything for me; but I changed it *shrug*

 

[MarsReefer]

I took extra care and made sure I got all the air bubbles out. It looks like that was the primary issue. In fact it looks like I probably initially calibrated it with a small air bubble in there as it has now way overshot.

Temperature has been dead stable the whole time so that shouldn't be an issue, but I did turn on the temp compensation to the 2.1 range as suggested. I think I will leave it for a day or two now and see if it stays steady and then if it does re calibrate

 

[Vivid Creative Aquatics]

I took extra care and made sure I got all the air bubbles out. It looks like that was the primary issue. In fact it looks like I probably initially calibrated it with a small air bubble in there as it has now way overshot.

Temperature has been dead stable the whole time so that shouldn't be an issue, but I did turn on the temp compensation to the 2.1 range as suggested. I think I will leave it for a day or two now and see if it stays steady and then if it does re calibrate

I reading like that (high 40s and 50s) usually does mean air or debris is on the probe. I would give it day or so to settle before making any changes.

And just for my own curiosity, can you overlay Temperature on the Conductivity graph, but do it for the period BEFORE the big spike.

 

[MarsReefer]

Here is from about 2 weeks ago when it first started dropping. The trend continues over the next two weeks as well.

 

[Vivid Creative Aquatics]

Here is from about 2 weeks ago when it first started dropping. The trend continues over the next two weeks as well.

OK - so definitely not temperature related. That's a pretty tight temperature gradient. only about t.4 total swing

During that period , did you chance salinity with a refractometer? Did it hold steady while the readings where dropping?

 

[MarsReefer]

Yes there is nothing in the tank and no light so I’m not doing any water changes, just curing my dry rock and getting everything stable. There is ato from my RODI but no other changes. Refractometer reads 35 consistently.

the probe is after my filtration which passes under a baffle so there really shouldn’t be any bubbles, certainly nothing visible.

 

[Lasse]

At least with the GHL probes - there seems to be some electrochemical processes taking place between water and the platina plates. as a result - small tiny gas bubbles seems to be created on the electrode plates. With placement in a steady current - these bubbles seems to be continues flushed away.

Sincerely Lasse