Salinity and Evaporation

[Jivatma]

So I know water evaporates naturally out of a tank depending on several factors. I approximate my evaporation to be about 2g per week on a 75g DT (approx 90g total). Does this sound about right?

As water evaporates, salinity goes up. This much is also clear. But how much fluctuation is bad? I try to test once a week just so I'm not worrying over numbers. But I have tested my salinity when water was low vs when high and i'm getting 35ish ppt when water is filled, and just over 36ppt when water is low. Does this much fluctuation over a week cause problems later on?

I am looking into an ATO for this reason, but I'm trying to get a sense of how urgent this kind of swing is. There isn't anything in the tank yet (still cycling), so livestock isn't in any danger, but I'd like to at least know before putting fish/coral in.

 

[Twoddler]

Stability is key, I would get an ATO in place, then it's one less thing to worry about...... sorry it's not the answer your looking for

 

[Uncle99]

Stability is key, I would get an ATO in place, then it's one less thing to worry about...... sorry it's not the answer your looking for

+1
When salinity fluxes, so does the rest of your chemistry.
So it’s very difficult to obtain stability.
ATO solves that problem.

2g per week, yup, that’s in the ballpark, varies as you said.

 

[Jedi1199]

OK.. so an ATO is nice to have if you can.. However, here is the secret.. You still have to fill the ATO reservoir every couple days or so. I use a 5 gallon bucket for mine and my 180 needs to be filled pretty much every other day. Same work, different setup. ATO's are cheap.. and the part I like is I can put the hose from the ATO into the first chamber of the sump so it mixes well before going into the DT. That said, my 55g does not have an ATO and I pour freshwater directly into the DT with no ill results.

Bottom line is this.. ATO will NOT save you work. It wont even necessarily keep your salinity any more or less stable... (provided you top off your tank daily). They are fabulous on nano tanks.. where a half gallon of evaporation means a higher salinity in a shorter period.. but on larger tanks, IDK if it is something really needed..

 

[alxrosco]

I have a 75 gallon and I add about half gallon every other day during the winter. Evaporation in the summer is less. I have done this for years and my corals SPS and LPS are just fine. Another option is to buy a dosing pump, like the new Red Sea, you could use 2 heads for a 2 part (Ca and dkh), one for Mg, and the last one as an ATO. I have read some people use them for continued water changes. At least the Red Sea and the Versa from EcoTech can handle large volumes.

 

[mike550]

@Jivatma for a fair amount of time I added RODI to my sump manually to offset evaporation in my 120G. I just had a tape mark on the sump and kept it close.

My first purchase for my tank was a Tunze 3155 ATO and a 5G container. Great first purchase for me.

 

[Jekyl]

So I know water evaporates naturally out of a tank depending on several factors. I approximate my evaporation to be about 2g per week on a 75g DT (approx 90g total). Does this sound about right?

As water evaporates, salinity goes up. This much is also clear. But how much fluctuation is bad? I try to test once a week just so I'm not worrying over numbers. But I have tested my salinity when water was low vs when high and i'm getting 35ish ppt when water is filled, and just over 36ppt when water is low. Does this much fluctuation over a week cause problems later on?

I am looking into an ATO for this reason, but I'm trying to get a sense of how urgent this kind of swing is. There isn't anything in the tank yet (still cycling), so livestock isn't in any danger, but I'd like to at least know before putting fish/coral in.

I would top off at minimum daily.

 

[ying yang]

I started my first saltwater tank 7 months ago and didnt install my ato i had until 2 months ago.
In the 5 months i had no ato installed,generally i used to wait till water change say and change 10% then fill my sump up with rodi water to put it upto my label saying maximum water line.it often got to just below minumum water level and on occasion it would get to point where baffle is going to last chamber water level close to making pump stop pumping so would top up before water change say so lost about 2- 3 gallons.
I know and read often that stability is key but my tank is 80 gallons plus about 70- 80 litres water in sump so probably around 20g sump that it runs at but when level was low and didnt top off,i would check salinity with my refractometer and salinity atill sake since last wc,which confused me as expecting the salinity to have rose,up until installed ato.i had maybe 5- 6 fish and only some common orange zoas and neon green paly's and never noticed any ill effects but i now got ato in a 5 gallon drum next to tank and just top it up a bit at weekly water change day so evaporates is around 2- 3 gallons a week i believe.
But as said its best to do stuff best we can so having an ato installed would be best practice and i think its simplier as just made a hole in the cap for the ato tube and power cable for ato to fit so less chance dog hairs and stuff like this get into the fresh rodi water in my drum.
But im still confused why my salinity didn't raise when my level dropped so low as i not got that big a tank and even if my refractometer isnt accurate it still inacurate to same degree all time so should show difference if get me ^_^