Salinity creep?

[mpderksen]

My SG keeps creeping up. Stuck on where to look, since salt doesn't just fall out of the sky. I have a DOS doing AWC at 1.5gal/day, but I just recalibrated it and it's spot on. I even bought a Milwaukee digital refractometer, and I've verified the 0.000 standard that it came with, as well as the 35ppt standard. My ATO water tests at zero. My skimmer doesn't fill more than every 2 weeks. My AWC barrel actually tests at 1.025. But in the last month, the tank has gone from 1.026 to 1.027.
The only thing left to try is catching both the input and output of the DOS during a cycle (68ml every 13 min or so) to confirm. But after that I'm really scratching my head here.

 

[thegrun]

Are you dosing two part? Doing so will raise your salinity

 

[Anemone]

Are you replacing evaporation with FW, or just putting more salt water in?

Kevin

 

[mpderksen]

Are you dosing two part? Doing so will raise your salinity

I read that elsewhere, but since I lost most my SPS in January, I'm down to adding 12ml/day. I would be surprised if that was enough to move the needle. However, I did switch from B-Ionic to BRS Soda Ash and Calcium. Maybe that's enough to do it? I'm about due to make up another 55 gal of New Saltwater. I'll make this next batch at 1.022 and watch the tank closely.



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[Anemone]

Are you replacing evaporation with FW, or just putting more salt water in?

Kevin

Still wondering.

Kevin

 

[Tripod1404]

The difference between 1.026 and 1,027 is very small. It is 34.5ppt vs 35.8ppt, that is an increase of less than 5%. What is the error rate of your refractometer, it might just be within the error rate.

Another possibility might be the sensitivity difference between flow and water level sensors of the AWC and ATO. If you AWC is removing and adding water before ATO kicks in to fill in evaporated water, it would basically be replacing small percentage of the evaporated water with saltwater. This would be very small for day to day change, but over a month, you might see its influence.

To give an example, say if your ATO kicks in once tank loses 3% water to evaporation but if the AWC does a water change at the point of %2, it will basically do a water change and fill 2% of the evaporated water with saltwater. In reality values would be much smaller, but filling 0.05% of evaporated water with SW will be enough to cause the increase you described over a month.

I dont know how you can do it, but you can prevent this by ensuring ATO fills the tank before a AWC happens. This why evaporated water will not be filled by AWC.

Another less likely option is if AWC is adding a little more than 1.5 gallon but removing a little less, it will cause the same effect.

 

[Tripod1404]

Still wondering.

Kevin

I think its FW, he said ATO tests 0.0 ppt.

 

[mpderksen]

The difference between 1.026 and 1,027 is very small. It is 34.5ppt vs 35.8ppt, that is an increase of less than 5%. What is the error rate of your refractometer, it might just be within the error rate.

Another possibility might be the sensitivity difference between flow and water level sensors of the AWC and ATO. If you AWC is removing and adding water before ATO kicks in to fill in evaporated water, it would basically be replacing small percentage of the evaporated water with saltwater. This would be very small for day to day change, but over a month, you might see its influence.

To give an example, say if your ATO kicks in once tank loses 3% water to evaporation but if the AWC does a water change at the point of %2, it will basically do a water change and fill 2% of the evaporated water with saltwater. In reality values would be much smaller, but filling 0.05% of evaporated water with SW will be enough to cause the increase you described over a month.

I dont know how you can do it, but you can prevent this by ensuring ATO fills the tank before a AWC happens. This why evaporated water will not be filled by AWC.

Another less likely option is if AWC is adding a little more than 1.5 gallon but removing a little less, it will cause the same effect.

However, there is no sensor for the DOS at all. It's going to pull 68ml, and add 68ml. Using the Avast ATO sensor, the level drops only the very slightest before it triggers. Like maybe a cup out of a system of 180 total? When it pulls out the 68ml, it's adding the new 68ml downstream at the same time.
And sorry if it wasn't clear, but my barrel with ATO top-off is RO water, no salt, and tested at 0.000. I have 2 55 gal containers. New water only goes in the first, and moves into the mixing station. I make about 100 gal each month


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[der_wille_zur_macht]

How does water move from the first 55g container to the second? Any chance of backwash which could cause the water in the first to end up with salt from the second?

 

[mpderksen]

How does water move from the first 55g container to the second? Any chance of backwash which could cause the water in the first to end up with salt from the second?

I have an MJ pump and tubing that goes from the first to the second. I plug it in manually (no Apex on this part) and remove the hose when it's done with the transfer. Also, as I've said, that water tested zero anyway.
Since the digital tester is so easy, I always test in triplicate too, so the differences are real, even if they are small.
The reason I'm extra concerned is that last summer i got really lazy on checking my salinity and ended up at 1.031 and lost most of my SPS, etc. In that case, I had the in and out of the DOS pump not matched (user error). Took 4 months to correct, so now I'm watching very carefully.


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