salinity dropping, how?

[reef tank 2.0]

My tank is still cycling (roughly 150 gallon in total, including sump), so this is a good time to figure out these quirks I'm running into.

9 days ago, i had the sand, rock work, and water in place. I dropped in a raw shrimp at that point, and am now waiting out the cycle process. At that time, my salinity was 1.025. Each evening, I am needing to top off with fresh RODI, roughly 1 to 1-1/2 gallons. I fill to the line, and move on. all good.

Well, for grins, today I tested my system salinity and I noticed it had fallen to 1.022. Never had that experience before. I could understand if i was adding too much fresh RODI. but even then, the gallon or two that i am adding, wouldn't make that much of a difference in salinity levels. At least I don't think. But that's not even in the equation at this time. I know how much water is missing, and how much I put back in.

I have added more salt to the system to get it back up to 1.025, but in the meantime......what else could cause the salinity drop other than water evaporation?
I will get it back up to 1.025, then I'll watch it each night.

I am using Reef Crystals (if that matters).
Using a refractometer for testing.

 

[TX_REEF]

Ca we get a listing of your equipment and ideally a video of the whole system top to bottom? The only things that come to mind off the jump are:

• faulty refractometer
• leak somewhere (which means saltwater is exiting the system and you're replacing with RO/DI, net loss of salt
• extreme wet skimming, are you emptying the skimmer cup very often? This could result in net loss of saltwater in theory

 

[reef tank 2.0]

im almost leaning towards the faulty refractor, but I'm not there yet. I did calibrate it upon receiving, so i know that's good. Or so I thought it was good.

Let me ask this, would water temperature effect the reading? That HAS changed throughout the process of adding salt. Due to me trying to dial in heaters to the correct temperature.

 

[TX_REEF]

im almost leaning towards the faulty refractor, but I'm not there yet. I did calibrate it upon receiving, so i know that's good. Or so I thought it was good.

Let me ask this, would water temperature effect the reading? That HAS changed throughout the process of adding salt. Due to me trying to dial in heaters to the correct temperature.

it's possible but, but I believe most refractometers have temperature compensation built in, and I think the temperature difference would have to be significant to make a noticeable difference

Reef Chemistry Question of the Day #264 Temperature and Refractometers

Reef Chemistry Question of the Day #264 Most reef aquarists that use refractometers are aware that the refractive index changes with temperature. Some handheld refractometers account for temperature by employing a bimetal strip inside them. This bimetal strip expands and contracts as the...

www.reef2reef.com

 

[rhitee93]

I don't think the minor temperature changes will affect a refractometer reading. At least it doesn't in my beer brewing hobby where we also use refractometers.

There was an article on here no long ago that demonstrated how much variation you could get in a refractometer reading if you pointed it at different light sources. It was shocking IIRC. Are you always looking at the same light when you calibrate and take a measurement?

 

[reef tank 2.0]

before the video, i'll hit on the other items.

I have ZERO leaks. the way the set up is right now, I would definitely see them if I had them. I have no water leaks, and I certainly see no salt creep around all the joints / fittings. I checked my drain line coming out of the sump that leads to the drain. That is completely dry. Besides, I'd hear that flowing into the drain if that was leaking.

My skimmer is on, but it isn't skimming anything. There is nothing to skim at the moment. I spose I could turn that off, but that's helping me get any remaining sand dust out of the system. The first few days, it was pushing some of that into the cup. But the cup never came close to filling up. I have it set on a dry skim level.

I don't have any dosers or reactors running. What I do have running in my sump is my return pump, 2 heaters, skimmer, and a powerhead. With a gyre in the display tank. that's all i got.

I believe there are some photos in my build thread of my set up.

 

[reef tank 2.0]

I don't think the minor temperature changes will affect a refractometer reading. At least it doesn't in my beer brewing hobby where we also use refractometers.

There was an article on here no long ago that demonstrated how much variation you could get in a refractometer reading if you pointed it at different light sources. It was shocking IIRC. Are you always looking at the same light when you calibrate and take a measurement?

yes, where the light source is that i use, is always the same one. so same light, same direction, and as level as i can make it.

 

[fishyjoes]

For me, I can never get a value I trust from a refractometer (at least the two I tried) so I gave up and got a tropic marin high precision hydrometer.
It's big, kind of a hassle to use, and easy to break - but I know it's trustworthy so it's worth all the downsides to me.

 

[reef tank 2.0]

Not sure if what you'd see here will help, but here's a video. With pauses in between. Sump is in the basement, while display is upstairs.

Ignore dirty glass, I will clean that when I do my water change after cycle.

click the photo, that should take you to the actual video

 

[reef tank 2.0]

You seriously have me questioning my drain line that comes out of the sump. I'm sitting here looking at the end of it, and it's dry. Nothing coming out of it. I'm wondering if it has a very slow leak that drips water throughout the day. But I would think it would be at least a drip if that were the case. If I unscrew the valve, I would think I'd see water coming out, which would indicate that my valve is not completely closing.

 

[reef tank 2.0]

So much for that....the valve is dry

 

[rhitee93]

You mentioned that you hadn't run the calibration recently. I'd take a reading with your calibration fluid again as a sanity check. Some of these refractometers are know to shift calibration frequently.

Scratch that. I'm not sure where I thought I read that you hadn't checked the calibration, but it wasn't this thread. However, it's worth checking if you haven't.

 

[reef tank 2.0]

Here's some nonsense for ya.

Going off what you just said....I decided to calibrate it again. I did that 9 days ago. (Keep that in mind)

I placed straight RODI on the lens. Looked through the eye piece, the level was -.015 from 0 (3 lines). what the heck!!

readjusted screw, retested. Now we're back at 0. That 3 line reading was the difference that I lost, or thought I lost. Again, what the heck

NOW, I decided to check the refractometer that I had during my last tank I had. Bought a new one for this set up since the old was in storage for so long. Checked the calibration on that one.....that was off a tad too. This gets a pass, since it hasn't been used in years. I adjusted the screw and now this one and the new one are both reading the same.

My salinity level is higher than I want, only cause I added more salt to correct the issue, that I THOUGHT I had.

I will add some more RODI to get it back to where I'd like, but I will monitor this over the next couple days to see if things change like it has.

Never had these issues before, so never thought much of it. Especially after calibration.

If anything changes, I'll be back. But I believe we (you guys) have figured out the problem.

Thank you

 

[TX_REEF]

Glad you figured it out!