Salinity Module not holding calibration

[maineultraclassic]

Over the past 2 weeks, I've had to calibrate the Salinity module about every other day. It will then start to drop down slowly, and I recalibrate it and it holds for the next day or so.
This add on is only about 1 month old, is away from any micro bubble source, and no snails or anything in the probe.

Any thoughts on what it could be?

Steve

[rimai]

I think your problem could be temperature variations.
Leave it there longer without pulling out or recalibrating and let's watch the charts.

[maineultraclassic]

When I first posted this question, my water was at 35.1. Now as you can see in my signature, it's saying 32.4.

I'm going to float the calibration fluid bottle in my sump, that will equalize the 2 of them exactly. Then I'll try it again and see how long that lasts.

A guy I work with also is having this same problem with his salinity module..........very undependable.

[maineultraclassic]

I floated my bottle of calibration fluid all day in my sump, then I calibrated my refractometer with it to exactly 35. I then tested my water in my sump, and it too was spot on at 35ppm. So I then hit the calibration setting for the salinity, and left the probe right in my sump. I came back about 2 hours later and hit "OK" and it is showing 35 right now.
We'll see how long it holds.

[maineultraclassic]

15 hours later, water at same temp as at the time of calibration............and it's already dropped 1.4 ppt.
Checked with refractometer, still at 35.

Is it the probe or the module?

[rimai]

What happens if you shake the probe inside the water?

[maineultraclassic]

Nothing at all.
I wiggle the probe in the sump and it doesn't change.
If I wiggle the wire at the module, it changes a little, but goes back to the original reading.

[maineultraclassic]

And still dropping.

I'm going to soak the probe in vinegar tonight to clean it, but I can't imagine it's dirty already with only a month's use on it.

[rimai]

Place it in a cup of tank water and let it build a chart for the next couple days.

[maineultraclassic]

I put it in a cup of tank water around 4:30 today, and it's still dropping.

Do I calibrate it in the cup of the water, or just let it be?

[rimai]

Yes, leave it there.

[rimai]

Did you do anything to the probe/controller yesterday around 4pm?

[maineultraclassic]

My fan was blowing on the cup of water, and it was evaporated..........so I topped it off.
I have it in a different position now so the fan won't hit it and evaporate as quick.

[rimai]

Ok. Let's watch some more then, but by the looks of your chart, everything looked fine in the cup.

[maineultraclassic]

Except for the actual reading.
I checked the water tonight in the cup with my refractometer and it's at 35, but it's reading 31.8 right now.

[rimai]

That's because we didn't recalibrate it.
The thing I wanted to see was if the readings would be dropping down as before and it hasn't.
In fact, it has gone up, probably due to the evaporation you mentioned.
But, let's watch the chart some more and see what happens in the next couple days.

[maineultraclassic]

I just topped off the cup again, it was down about 3/4" - 1" from the line I drew.

[wolffman64]

I've had the same problem with my salinity probe, ever since I installed it, it's all over the place. I had to buy a new probe, but I haven't installed it yet. I have tried all the actions above but still the same problem.

I'll let you know if my new probe is better after the weekend (will install it tonight)

[rimai]

Yeah, I can see the module and probe seem to be reading just fine.
There is gotta be something in the tank that is causing the reading to drop.
Are you sure there are no bubbles?

[maineultraclassic]

How can you even say that you can see the module and probe reading just fine?

The water is 35ppt, yet it's reading 30-31.5........that doesn't seem fine to me.

The guy I work with is having the same exact issue with his, he doesn't trust it any longer......nor do I. Wolffman is having the same issue, I'm sure his water isn't 26ppt.

How are you supposed to trust a probe to monitor your salinity, maybe use it to add fresh water or salt water as needed............when it reads 4-5 ppt low at all times.

[lnevo]

He said earlier that when you first started with the probe in the cup it wasn't calibrated. It was 31.8 the other day... Looking at the graph (http://forum.reefangel.com/status/chart ... filter=sal) It's been at ~30ppm since you moved it to the cup. Aside from evaporation and the couple of top-off's that you've done, the salinity hasn't dropped more than a bit below the 30ppm mark. And it hasn't been dropping as it was when it was in your tank...

If you want to see a more accurate number, put it in the cup, do the calibration, then leave it in there, topping off regularly and you'll see a more stable 35ppt. Previously when it was in your tank you went from 35.1. to 32.4 in a day...

[rimai]

Exactly.
It doesn't matter what number it is. All we were looking at was trend and it has been stable instead of dropping and going up.
If you must see 35ppt, place the probe in the cup, go through the calibration and keep evaporation at a minimum, like covering the cup with plastic or even aluminum foil.
You will see that the readings are going to be what you were expecting it to be.
By using the cup instead of your tank, we know for sure there is no bubbles, no temperature swing from a nearby heater and no interference from any pumps.
The readings are highly sensitive to temperature and air bubbles.
This is a clear example of how temperature affects the readings:

Temperature

temperature.png

Salinity

salinity.png

My salinity is not really 27ppt either, but I really don't care seeing 35ppt in the graph as much as I care about trend and if it is deviating from about 27ppt.
As you can see, salinity readings change by almost 2ppt when the temperature varies by about 4 degrees.
The graphs above are unaffected by air bubbles, because it comes from my own tank and I have my DC pump controlling my return flow to match my drain rate, so I know for sure there is zero bubbles.
But, micro bubbles have the same effect. The more air bubbles, the more the readings can deviate, not to mention that they tend to accumulate inside the tip cavity. So, place your probe after your sump bubble trap.

[maineultraclassic]

My drain line goes into my filter sock all the way to the left with the skimmer, then there is a 3 panel bubble trap, then my fuge area, then another baffle, and the probes are mounted all the way on the right. I have no micro bubbles in the far right section of the sump, what makes it thru the bubble trap doesn't make it thru the fuge.

I'm going to do a fresh cup of water, covered and sealed with saran wrap, and poke the probe thru so it's tight with no evaporation. Then calibrate it in there and leave it for a while.

[maineultraclassic]

I was out shopping yesterday and spotted a small Fluval pre filter that is the perfect size to slip over the probe.

I cleaned up the sump today, moved somethings around, and put the probe back in the tank and calibrated. I squeezed all the air out of that foam pre filter sleeve and slid it over the probe just as another added guard against micro bubbles if that was the issue.

So far it's holding steady, time will tell if this will work.

I also removed my reactor that I was using for carbon for a while, but recently added some GFO to it. Then I started thinking that the GFO may have been causing the issues?

If it starts dropping again...........what's next?

[rimai]

Can you please post a photo or better yet, a link of the item you bought just so people reading this in the future can refer to?

[maineultraclassic]

I bought the smallest size they had, ot sure if it will work or not, but time will tell. Cost me 70cents at Petco, so it really didn't hurt much either way.

Steve

[lnevo]

How often does your ATO go off? Your salinity looks pretty consistent since yesterday around 1pm. It is creeping up every so slightly since then (started at 35, now at 35.5) So it seems the downward trend is not showing it's head...wondering if we're just seeing the evaporation now.

[maineultraclassic]

Looking at my log, it goes on a couple of times a day. I'm topping off my top off container with about 2qts of water per day right now.

[lnevo]

Ok cool. So then so far the chart for salinity looks good. Fingers crossed. How big is your tank btw?

[maineultraclassic]

Display is a 54 corner, sump is a 30 breeder

It seems the salinity is creeping upwards now, going to have to check this afternoon and see what's happening.