Salinity stability: what's the harm? A discussion.

[Sk8r]

We drink fresh water; if we drink salt, we die, as our bodies can't cope with the salinity...our kidneys handle fluids, getting rid of fluid and waste, and if we get too much sodium (salt), we get blood vessel rupture, buildup of fluid in the brain, etc, in a situation that will be lethal over time, ruptures happening because of the difference in pressure on either side of fragile membranes. This is called 'osmotic shock.' You can look that up.

Marine fish have the ability to cope with salt and salinity changes without distress as long as they're slow. Different areas of the ocean do vary a bit in salinity...and fish that are not comfortable can move. Fish can tolerate a relatively rapid drop down to a survivable level of 1.009 (no lower than that). But they DON'T cope with rapid UPWARD change in salinity. If salinity is rising, you have to limit that rise to no more than .002 every fifteen minutes, and no higher than 1.026. This gives the kidneys time to do their job and try to equalize the situation, so that their internal tissues AND the surrounding water are in balance. If too rapid, again, rupture of blood vessels, and ultimate death from kidney damage, as kidneys can no longer do their vital job, even when the balance is restored.

Corals have a better method of self preservation: they expel all water and wait---but ultimately they need to take in water again and expand, and their survival range is narrower: they live from 1.024 to 1.026.

As you can see, ANYTHING that bounces the salinity rapidly up or down is Not A Good Thing. In the wild, fish can vote with their fins and move if they're unhappy. But what happens if your daily evaporation is, oh, say, a gallon, and every day you pour a gallon of ro/di straight in. That's a bit of a rapid bounce. If you were gone for the weekend---that salinity concentrates higher and higher the more water evaporates. [Same, btw, goes for any meds or additives.] So here is this fish sitting at a high salinity, and your throwing in more than a gallon of water is going to DROP the salinity, which is way safer than raising it...but it's happening a lot. Poor fish get hyped slowly---then plunged downward suddenly over and over and over. Corals can't take it, and neither can inverts that have shells that DON'T sweat, as fish do. While it won't kill fish, it's over all easier and likely healthier for your fish to have trustable, stable water. So while you're worrying about feeding your fish the most scrumptious, proper things to make them thrive---don't forget their water supply, which is critical on so many levels.

An ATO (auto topoff unit) is your solution, and there are a number on the market that don't require a controller or doser. They add water all day long, by the teaspoon, not by the gallon, so salinity balance is constant, and automatic. They work with and without a sump. And there are some that work for nanos. If you're going on vacation---just put a really large barrel of ro/di beside your tank and you can be gone literally for weeks, even for a large tank, with an autofeeder or two handing out flake and pellet. Managing an ATO is, however, a bit of a learning curve---and you are LIKELY to make mistakes (forgetting to plug it in, bumping the sensor out of position, etc) ---so don't plug in a brand new one and immediately dash out the door for a week's vacation.

[bdunn12]

Awesome info. Got my ATO on the way! Thanks.

[nereefpat]

Good discussion.

I've thought about building an ato but the math doesn't seem to tell me to worry about it. I'll elaborate:

Rough figures here of course. My 125 evaporates about 1.5 gal per day. 1.5 / 125 = 0.012 or 1.2%. We'll use a s.g. of 1.025 as baseline. An increase of 1.2% each day would raise my s.g. by 0.0003. So after 3 days of not topping off, my s.g. will raise from 1.025 to about 1.026. Of course the effects are compounded because the volume of the system diminishes each day.

I haven't ever tried to keep sps, so there is a caveat there. My fish, lps, and leathers don't seem to mind. Like you said though, the commutative stress may cause some issues in the long run.

[Sk8r]

And...if you have to go out of town for some reason, that can be a problem. Local humidity matters. I lose about a gallon a day from the 55; same from the 105, but it is totally glass-covered.
The lower evap rate however, becomes a problem if you have a lot of stony coral and would rather have kalk in the ato reservoir (which needs no special equipment, just dump it in) than have a kalk reactor, which involves a co2 cylinder and a reacter cylinder...quite the rig.

The main thing I would worry about for your current situation, however, would be if you have to leave it unexpectedly for a fairly lengthy trip with nobody to tank sit. Losing 1 gallon is nothing to a 125, but it gets more of a problem when water level in the sump begins to fall below certain levels re heater, etc. Your current rise-fall is probably no greater than some areas get with tidal flow near a river.

[nereefpat]

Originally Posted by Sk8r

The main thing I would worry about for your current situation, however, would be if you have to leave it unexpectedly for a fairly lengthy trip with nobody to tank sit. Losing 1 gallon is nothing to a 125, but it gets more of a problem when water level in the sump begins to fall below certain levels re heater, etc. Your current rise-fall is probably no greater than some areas get with tidal flow near a river.

You're definitely right about that. My pump will suck air long before my salinity rises to unsafe temps. My thermometer is in a constant level chamber, along with the skimmer

[chefbill]

Originally Posted by Sk8r

. Managing an ATO is, however, a bit of a learning curve---and you are LIKELY to make mistakes (forgetting to plug it in, bumping the sensor out of position, etc) ---so don't plug in a brand new one and immediately dash out the door for a week's vacation.

I think thus is great advice for ANY change. Don't make any change that you can't monitor several tines a day. Bad things rarely creep up on you, just as good things don't happen overnight.

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