ATO lowering salinity?

[york1]

Hanna makes a salinity tester. Digital and as long as you calibrate it every now and then has worked well for me.

Marine Salinity Tester

Hanna Instruments HI98319 Marine Salinity Tester measures conductivity (EC) to determine the salinity of natural and artificial seawater within seconds.

www.hannainst.com

 

[Trizzino]

What’s you salinity immediately after a water change?

 

[ActiveAngel]

ATO will never drop salinity if the tank volume is constant. That said, it doesn’t mean that salinity can’t drop while the ATO (and/or other operations) are taking place.

This is because “Auto Top Off” simply tops off (I.e., adds) water. There are only a few ways to decrease salinity. 1) Remove salt, or 2) add non-salt (e.g., water). However, if you were to follow #2, also called dilution, this would only take effect if you added enough to significantly increase the volume.

Now what are some potential explanations:

• Lots and lots of salt creep. Unlikely to happen in these quantities unless you’re talking about salinity decreasing slowly over 6+ months. It seems like you’re suggesting it’s decreasing faster though.
• During regular water changes, the ATO may not be disabled. If you forget to disable it, then the ATO is dumping freshwater into your tank, lowering the salinity. Moderately likely. It’s a common mistake.
• Salinity isn’t decreasing. Your refractometer may just not be calibrated correctly. Moderately likely also, but it’s easy to double check, and I don’t think this is it.

 

[silentdeath5]

Since it hasn’t came up yet. Any salt creep around the tank that would suggest a small leak? Even a drop every few seconds would eventually add up to something within a week with that small a volume. Less likely but an idea

 

[ichthyoid]

Running a skimmer and an ATO result in a gradual salininity drop. It’s salt water out and fresh water in.

Doing water changes, using the same salinity water, doesn’t add back any of the lost salt.

 

[ActiveAngel]

Good points! A slow leak is another possible/unlikely option.

But the reason I suspect salt creep/loss as less likely is that should be about ~0.9 lbs of (dehydrated) pure salt. Once factoring in water content, it gets a bit bigger. One would probably notice mounds of salt that big around their aquarium... not that we all don’t have tons of excess salt around our aquariums, lol.

This at least gives us an idea of the amount of salt being regularly lost here.

 

[ichthyoid]

Good points! A slow leak is another possible/unlikely option.

But the reason I suspect salt creep/loss as less likely is that should be about ~0.9 lbs of (dehydrated) pure salt. Once factoring in water content, it gets a bit bigger. One would probably notice mounds of salt that big around their aquarium... not that we all don’t have tons of excess salt around our aquariums, lol.

This at least gives us an idea of the amount of salt being regularly lost here.

Agreed, & quick math says that should be a bit over 3 gal, yes? Or, 0.05 gal per week avg. About 3/4 cup liquid per week avg.

If the salinity dropped over the 4 months time mentioned in the initial post, that’s entirely possible (if not probable?).

 

[ActiveAngel]

Agreed, & quick math says that should be a bit over 3 gal, yes? Or, 0.05 gal per week avg. About 3/4 cup liquid per week avg.

If the salinity dropped over the 4 months time mentioned in the initial post, that’s entirely possible (if not probable?).

Agreed. But I think he’s losing salinity over a few weeks, and is constantly readjusting. And that the tank is 4 months old.

But agreed; if this loss was spread out over 4-12 months... this would become possible. And assuming one was regularly vacuuming/cleaning up the salt.

 

[ichthyoid]

Agreed. But I think he’s losing salinity over a few weeks, and is constantly readjusting. And that the tank is 4 months old.

But agreed; if this loss was spread out over 4-12 months... this would become possible. And assuming one was regularly vacuuming/cleaning up the salt.

My calc’s were based on 4 mo’s.
I didn’t see where he was readjusting salinity.

 

[ActiveAngel]

No worries. Yeah, I got you.

Specifically, we know that “over a few weeks salinity will drop several points”, and that the tank is 4 months old. Assuming this is an issue, and not just a 1 time event or potential-miscalculation, I concluded he must be readjusting. You didn’t miss anything; he was never explicit with readjusting.

 

[ichthyoid]

All I see is he does ~25% water changes every 1-2 weeks using 1.026 water, has an ATO, and dumps his skimmer cup about every other week.

At an estimated volume of 1 1/2 cups of skimmate avg. dumped every other week, I think we see what’s happening here.

He needs to adjust his salinity upwards. I’d probably just add a little salt to the ATO water.

We can calculate that for him also, if he’d like?

 

[ActiveAngel]

All I see is he does ~25% water changes every 1-2 weeks using 1.026 water, has an ATO, and dumps his skimmer cup about every other week.

At an estimated volume of 1 1/2 cups of skimmate avg. dumped every other week, I think we see what’s happening here.

He needs to adjust his salinity upwards. I’d probably just add a little salt to the ATO water.

We can calculate that for him also, if he’d like?

No worries. You can read his initial post; that’s where I just pulled his details from.

Is he dumping 1.5 cups of skimmate every other week!? Wow! Sorry, I totally didn’t know that. On a 20g, that sounds like a feeding (or other dissolved organics) issue. I don’t get that cumulative skimmate on my 3 tanks, and definitely not on the nano 20g... but my skimmate is super thick. I would guess his is very (salt)watery, which would explain the loss of salt. That’s also a pretty darn big reservoir for what I’d expect on a 20g’s skimmer, even an HOB. Are we sure that’s accurate? You’re totally right that this information changes the game, metaphorically speaking.

Even so, I would disagree with adding salt to the ATO. Instead, if we fix the issue with dissolved organics and dial-in the skimmer, we will solve two issues in one... and without risking increasing the salinity above 1.026 after the tank runs low on organics and the skimmer stops pulling as much.