[tibbar's reef]

I have had a few saltwater tanks through the years, but have never had such a problem with evaporation of water. I have had my 75 set up for about a year, doing awesome!
I add on average 5-10 gallons a week, sometimes more, is this normal? Temp 75-78 degrees-t-5 flourescents about 4-5 inches above water level.
I was thinking of building a pretty much inclosed top for it? any suggestions?

[glampka]

Open top tanks do have a tendency to evaporate more water. I had a 12 gal Aquapod with the enclosed hood - added water maybe once every 2 weeks. Now I have the Aquapod with the MH light - adding at least a pint every day.
Glass covers were nice because they cut down on evaporation but they do more harm than good. Hurt gas exchange & keep in heat. An enclosed cover may cut down on evaporation but at the expense of adding heat to the tank. You'll want to put an exhaust fan in there to keep things cool.

[pogodzib]

Yes, it is normal for reef tanks, or any tank with strong lights and no glass top. I evaporate 5 gal/day on my 220 gal tank during the winter. Come summer, I'll probably evaporate around 8 gal/day. The evaporation is good during the summer since it helps keep the tank cool. During the winter it's not a s beneficial, but adding a glass top in between would cut down on the light making it into the tank by 10-20%. Adding an enclosed canopy will help some, but come summer, you may not want your canopy fully enclosed because of heat issues.

[unclejed]

The glass top is no problem if you factor in the holding of heat and compensate for it, I have glass on my 55 gal. and adjusted the heater accordingly (a few degrees lower). Another thing that aids in evaporation is if you have your flow set up to agitate the top layer of the tank water. The catch is, this is good for a better oxygen exchange and keeps scum from sitting on top of the water. Adding fresh top off is good but, remember, when you add a good quantity as you are, keep an eye on your salinity.

[ozzychas]

the way i understand it, water evaporates not the salt.

[pogodzib]

Yes, only water evaporates, so you replenish it with fresh RO/DI water.

BTW, because I evaporate so much water, I use an ATO device so the water drips in whenever the water starts to drop so the salinity is always constant.

[unclejed]

Sorry, thought you would understand about the salinity remark I made. True, water evaporates not salt, however. if you keep adding fresh water, over time you dilute the salt content. My salt got away from me (before I bought a refractometer) and to reduce the SG I was doing 4 gal. every other day fresh water changes to get the salt down. If you are loosing a good quantity of water through evaporation, it is essentially like doing little changes and adding only fresh water, hence my warning to watch your SG.

[pogodzib]

The salinity should never change if the water level within the tank stays the same. Since only the water evaporates (not technically true, but close), you can add as much makeup water as it takes without the salinity fluctuating. I've added over 200 gal of makeup water to a 125 gal tank between water changes and the salinity read 1.025 at the beginning and still 1.025 after a month's worth of evaporation and topoffs.

[Jason L]

I agree with Brian i lose about 1 to 1 1/2 Gal a day to normal my tank run 79 am and then up to 83 pm

[pogodzib]

Skimmate, on the other hand, will lower your salinity over time, if you skim very wet and heavy. Maybe that is why your salinity dropped.

[icu-travis]

i agree! some say skimming wont affect Na or SG but when i upgraded my skimmer i started on max skim mode and my salinty droped overnight.

[bnhaus]

Yes, very normal