ATO causing salinity variations

[rmcaum]

I have a 29 gallon tank without a sump. It has a Tunze ATO. I have a seven gallon reservoir that lasts about three weeks or so. Over the course of the month, between water changes, the salinity dips from my desired level of 1.026 to around 1.024 or so because of skimmate removed through the skimmer. If I want to correct the the salinity back to 1.026 I can make some super saline water to add during a water change, but this doesn't do much for the stability of the tank. One answer would be to do more frequent smaller water changes with slightly less elevated levels of salinity to reduce the amount of fluctuation. Of course all of us want to do fewer water changes, so that isn't what I am looking for. Has anyone ever added salt at a very low level, say 1.010 or something to their top off water to correct for skimmate collection variations. This would be challenging given the variance in evaporation rates and sometimes even fluctuation in skimmate collection (it is a hang on the back after all.) anyone have a solution for this issue? Anyone have a calculator to compare top off water used vs skimmate collected to produce a number for salinity in top off water (if it was consistent of course?)

 

[Diamond1]

Not sure about adding saltwater as top off. It would seem a little dicey to me to do it that way and try to figure out the formula for evaporation and salt loss due to your skimmer removing varying amounts of salt. I would suggest running your skimmer as dry as you can so you are minimizing the amount of salinity lost through skimmate, and continue to make any adjustments during water changes.

 

[spacetime]

Don't just add salt or add saltwater to your reservoir. If you can just turn off your ATO until evap gets you were you want 1.026. Then replace the water evaporated in your sump with 1.026 SW until it the water line hits the ATO sensor. If you can't wait that long then top off with salt to make sure you don't run your pumps dry.

 

[mike007]

I have the same ato and I have never had a issue like this. Since the salt stays in the tank adding small amounts of ro should not alter the salinity that much. If you are only doing once a month water changes and your skimmer is pulling the salt out you may want to increase your water changes. I would not worry too much about 1.024 from 1.026.

 

[rmcaum]

Thanks for all the responses! I don't have a sump, or I don't think it would be an issue. I have fill line set so that the water line isn't visible in the display. If I had some variance there I could replace any saltwater loss from the skimmer before there was any noticeable change in the display level. I agree that it would be dicey since the amount skimmate varies on tank conditions throughout the month. Running dry with the skimmer would be great, but I have nitrate and phosphate issues so I skim quite a bit. I also just started dosing nopox so I am not sure how that will affect the skimmate as well. I think the answer is as advised to do more frequent water changes, or at least add about 4 cups of saltwater every time I empty the cup. I guess that is a little more maintenance free than having to manually top off every day. I think that the variance in skimmate would prohibit any formula from remaining accurate for the duration between water changes. If anyone has any more ideas I would love to hear them. I guess I don't worry that much about the .01-.02 shift over that period, just thought that stability is a large factor in success.