what the...? HELP!

[craqerjaq]

ok well I'm confused then about the refractometer...because I tested the cold water straight from the brute and it had a reading of nearly 40ppm and when I warmed the same water still in the dropper...it went back down to 36ish. I wipe the glass completely clean each time not even a smudge left or it will bother me. I can't think of any other reason besides temp that would affect a reading so...but you're right it says ATC in the info. now I'm even more confused.

[Ninong]

First, please stop using ppm when you obviously mean ppt. There's an enormous difference.

Here are a couple of tips on using any refractometer, including an ATC one.

Always make sure that the glass is perfectly clean.

Always hold the dropper with the water to be tested upside down in your hand for a couple of minutes to allow the water to reach ambient room temperature before dropping two or three drops onto the glass plate.

Make sure that the water on the plate covers the entire plate after you bring down the top glass lid. It usually takes only a couple of drops to do this.

Whenever you get a reading that seems off, retest twice more until you are satisfied with the reading.

[craqerjaq]

well what do ya know it says ppt inside there haha must have overlooked that...been thinking about the test kits.

I've done exactly those things each time I tested but I don't think I warmed the water when I got the weird reading. Right now it's where it should be.

but now I'm wondering about something else. as water evaporates from the display tank or as dried salt builds up from the natural splashes of water near equipment and stuff...will that affect salinity levels in the tank? The reading I am getting from the tank now seems just 1-2 ppt lower than what I remember it say a week ago. Will something like that have a big impact on life in the tank? I know invertebrates are sensitive to changes...what about everything else?

[Ninong]

but now I'm wondering about something else. as water evaporates from the display tank...

Evaporated water is replaced with freshwater (topoff) because salt does not evaporate, it remains in the tankwater. This is why evaporated water should be replaced daily, one way or another. This is especially important on really small tanks, such as nano tanks (20 gallons or less), because waiting to top off every third on fourth day would result in measureable swings in salinity.

...or as dried salt builds up from the natural splashes of water near equipment and stuff...will that affect salinity levels in the tank?

Yes, but in the opposite direction. Evaporation leads to higher salinity in the tank. "Salt creep" leads to lower salinity in the tank because you are removing salt. The change in salinity due to salt creep is very, very small compared to the change in salinity due to evaporation because the amount of salt lost to salt creep is very small compared to the total amount of salt in the tank. If you were to set up an automatic topoff system to replace evaporation with freshwater (or limewater) and didn't bother to monitor your salinity, your salinity would gradually drop but it would take quite a while for salt creep to have a noticeable effect.

Another way that the salinity in your tank is gradually lowered, although this is a very small effect, is through skimming. The wetter you skim, the more saltwater you are removing from the tank. If you skim extremely dry, then this effect will be extremely small and take a very long time to show up. If you skim very wet, and remove say a pint or more of wet skimmate per day, then the effect will build up. That's because the saltwater that you remove in your skimmer cup is replaced by freshwater when you top off the tank.

That's why it's important to check your salinity from time to time. At least weekly in the beginning and maybe every other week later on once you are comfortable that your salinity doesn't vary very much, if any, in just a couple of weeks.

The reading I am getting from the tank now seems just 1-2 ppt lower than what I remember it say a week ago. Will something like that have a big impact on life in the tank? I know invertebrates are sensitive to changes...what about everything else?

Echinoderms (sea stars, etc.) are the most sensitive to changes in salinity, especially sudden changes. A change of one or two parts per thousand over two or three days is certainly not a problem but not something you would want. A change of two or three parts per thousand over two or three minutes would be a problem for some of the stuff in your tank.

Usually the only people who run into trouble on this issue are people with smaller tanks (especially 20 gallons or less) who leave their tanks unattended for three or four days. Maybe they just have a relative feed the fish every day but not top off the water. Then when they get back, the water in their 20-gal tank is 2" lower. To make matters worse, they immediately add freshwater to bring it back up. So their salinity gradually rose over three or four days and then it's instantly brought back up to where it was previously. Not cool.