The best salinity setting...and why. A discussion.

[Sk8r]

Reef salt at a half cup salt per gallon works out at about 1.024. The 'good range' is from there to 1.026.

Fish-only salt works out to about 1.020, and again, 1.019 up to 1.025 is ok.

Now, where, within this range, do you want to set your tank?

The answer lies in the typical mechanics of a fish tank: it tends to lose water to evaporation. Salt does NOT evaporate. So as your tank loses water to evaporation, salt concentrates---ie, its level RISES.

Now, topoffs add water: a topoff accident may add too MUCH fresh water, which dilutes your salt even more. If this happens, correct it by removing some water and adding salt water (perfectly clear salt water: undissolved salt can burn fish gills and corals) ideally to a sump. Raise the salinity no more than .oo2 per 20 minutes. Critters can take a suddenly DROPPING salinity; but a rising one is dangerous. GO slow!

Now, regarding evaporation, the natural process: an ATO compensates for this, adding fresh water by tablespoons, not buckets: much nicer for the fish and corals.

BUT---and the point of this post---where do you want to set your basic salinity? My advice (since you are NOT going to have a topoff accident, because you are going to use, say, a dual float switch, that cuts off properly) is to set your salinity at the bottom of the range (1.024, say) so that evaporation will not push your salinity up OUT of the safe range.) Typically the ATO will cut on before the salinity has risen more than .001, but some are not as prompt. If you have set your salinity at 1.025, and your ATO is sluggish, you'll see it at 1.026 or more before it gets corrected.

Make your own call on this, but just understand the basic principle: too much water dilutes the salt; too little concentrates it. Set your salinity to give yourself the most leeway within the appropriate range, and above all, do NOT set up an ATO for the first time just before you leave for the weekend. There is a learning curve. Have a refractometer (they last for years, properly cared for)---and be precise. Set up your ATO and learn how to care for it.

That way your tank stays stable and your water stays proper.

 

[JMorris271]

Sk8r
Suppose the salt is at 1.016. What is the best method to determine the amount of salt needed to bring it up to 1.025. Test the water after each ato addition and then once the correct level is reached, dump the ato and refill with fresh RODI?

 

[Sk8r]

If you are talking about a bucket of water with no live things involved, the fastest practical way is to put a strong pump into the bucket, turn it on (mixing pump) and be sure all salt has already dissolved, then add more salt, mix overnight, add more salt, etc, until satisfied.
If you are talking about a salt mixing bucket, incidentally, it is as important to accurately measure the ro/di as it is to accurately measure the salt so you don't have to go through this. Use a permanent marker to mark x-many precise gallons on the side of the bucket, then add x-many half cups of salt. For example, I have a precisely marked 32 gallon mixing bucket, and put in 1 gallon of reef salt (which is 32 half-cups). Mix overnight and I'm generally good to go.

If you are trying to up the salinity in a functioning tank, just top off only with 1.030 salt water until you reach the desired 1.025. The little amounts of high salinity water will spread out, and you'll get there doubly fast as, first, evaporating ro/di leaves your tank and strong saline comes in. Don't let the salinity rise more than .002 in any given half hour, as a ball park. Fish cope well with FALLing salinity, but can't survive a too-rapid rise.

The short cut to the math of these measurements is called 'conversion tables'. Google the internet for cups in a gallon, liters to quarts, yards to meters --- every measurement converted to any other.

 

[JMorris271]

Something I have wondered about, when measuring salt, are you reading the measurment with a level cup or a heaping cup?

 

[DivingTheWorld]

Something I have wondered about, when measuring salt, are you reading the measurment with a level cup or a heaping cup?

The measurements on the bag are assuming level cup. It just depends on what you're trying to measure to. I shoot for 1.0264 and vary between 1.0261 and 1.0265. I mix my water change water to 1.0264 and that usually means heaping cups vs level cups.

For raising the salinity in your tank, you'll eventually figure out what yours takes as every tank size varies. Make sure to keep notes. I know with mine, 1/2 cup will raise my salinity about 0.0003. I just mix the 1/2 cup into about half a gallon of R/O water and when ready pour it into my overflow. As the tank water evaporates, it slowly raises the salinity.

 

[Sk8r]

particular species and specialty tanks may require certain conditions that need to be held: as you settle on what sort of tank you want, and what you want to keep, you provide those conditions and keep them steady. The ocean itself has variations in salinity, not to mention rainstorms and upwellings and currents. Our tiny tanks, however, are a much, much smaller slice of ocean, in which the occupants cannot swim away from unpleasant conditions. Study your species, look them up on the internet, and automate as much as you can, because you can't stand by 24/7/365. This doesn't mean a controller is mandatory: I've never used one, just timers and float switches and such, nothing technical at all.

 

[anthonys51]

so a fish can go safely right out of a bag of water from 1.027 to 1.025

 

[1sttimer]

I have a mark on my tank that indicates the max water level. If it's Below that when i do a water change i'll put another mark where the water actually is at the moment of the water change and fill it with saltwater i've prepared the night before till that mark and then top it off till my "full" line with distilled water. I'm always within 1.023-1.024.