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Hi, I have had my tank in working order w/ 5 Damsels in it for about 4 weeks now, obviously I have had some water evaporate and want to ad some water. How do I do this without hurting the fish and without changing the salinity? Also I would like some advice on when is a good time and how is the best way to do a water change.

----- Original Message -----

Reading what y'all have to say on topping off for water evaporation, should it be done with fresh not salt water? I have been using salt water. What is best and why?

Don't look now, but your salinity has already changed!  As water has evaporated leaving less in the tank your concentration of salt has increased! Solution is easier than explanation--add water, preferably R/O and aged… Just be sure of no chemical contamination, (chlorine, copper, etc.).  You might want to think about using some sort of topping system to monitor and correct this problem on an automatic basis.  I was able to buy a very expensive hospital dosing-pump with excellent control features for $50 at an auction.  Commercial "marine hobbyist units" I've seen tend to run 2-4 times this cost but are designed to plug and play.

You should be topping off your evaporation with fresh water, not salt water. The reason being, salt does not evaporate - only the water does. Your salt content is still there. If your are topping off your evaporated water with salt water, you are consistently adding to your salt water content. Am I making sense? Somebody help me here....

Your salt water is only going to increase and increase until you have levels that are much too high. To experiment, take a small glass of salt-water mixture, stir it up and then let it set for several days. Your water will evaporate, but all your salt will settle to the bottom. And as your water evaporates, your salt level will increase, therefore you need to add fresh water to maintain the level of saltwater that you had before.

You should add "makeup water" (i.e. fresh water) to your tank on a daily basis, to compensate for evaporation. Here is a simple way to do this accurately, and without the hassles of checking with the hydrometer every time: Firstly, make sure the water salinity is correct (1.024 - 1.025 at 25C) and the tank is filled to the desired level. Then stick a small piece of tape (or make a small mark with a pen) on the side of the tank at the water level. This water level should then be maintained by the addition of fresh water only. You should preferably not add all the make up water in one go, but rather add smaller amounts a few times per day (the ideal is to drip the water into your sump at the same rate as the evaporation).

You should replace evaporated water with "pure" fresh water. Water filtered through a RO or DI unit is ideal. Alternatively, you could use bottled "distilled" water, but make sure that it does not contain copper. You could also buy bottles of "designer water", but this is usually very expensive, and sometimes contain a high amount of impurities. As a "lower grade" alternative, you could use one of those water purifier jugs sold for home use (e.g. Brita). Lastly, if you don't have any alternative, you could use normal tap water. This will contain chlorine, etc, and you should aerate it for about 24 hours before use. Just bear in mind that non-RO/DI water usually contains some dissolved minerals, which could build up in your tank over time, contributing to algae problems.

Salinity changes should be made very gradually. If you discover an unacceptably high (or low) salinity level, don't suddenly add lots of water to correct this. Your animals can "acclimatise" to some change in salinity over time, but the osmotic shock of a sudden change in salinity is very dangerous.

You should also replace some of your salt water on a regular basis, something in the region of 10% to 20% of the tank's volume every two weeks. This dilutes the harmful build-up of pollutants, and replaces used up trace elements and calcium.

From: WS

I think that you need to buy a basic book on marine aquariums. If you do not have any knowledge of water chemistry, you and your fish are going to have real problems.

When water evaporates it leaves the salt behind so the specific gravity will increase. You need to refill the tank to nearly where the water was previously, with fresh water, preferably RO or de-ionised. Try to refill slowly. Leave it for a couple of hours and then check SG again and make any necessary adjustment with either fresh or salt water. You should check SG every week. If you lose a lot of water through evaporation, you should top up the tank more frequently to avoid any major variations.

From: DM

I will start off by saying that the water is the only thing that evaporates out of you tank. Keeping this in mind: as the water evaporates, the salinity becomes higher. The goal is to keep your salinity level, by adding plain water back in as it evaporates, at the same rate. I don't add water constantly, but some do at a drip. This keeps the salinity perfect all the time. I add water every day, this amount is small but it is better to add a little at a time then a lot. In 4 weeks your tank probably has lost a lot of water. You need to add RO water (Reverse Osmosis) as soon as possible. I would add it at a slow rate. Find something that you can drip it in with or at least drizzle it in very slowly. That way you won't change the salinity to fast. After you get your tank filled back up and make sure the salinity is correct, keep the water topped off as best as you can.

Next question: I do water changes every two weeks on my reef tank, about 20% or so. You have to premix your salt and water at least 12 hours before you perform your water change. Put a power head or a bubble stone in the bucket to circulate the water around for the 12 hours. I mix mine up the day before. Then, you just remove however much water you want (10-15-20%) from your tank. I usually try and add the new water slowly. I have added it fast and have had no problems though. Make sure the temperature is the same though if you add it fast. After that turn on all your equipment and your water change is complete.