I don't understand this--rising salinity

[rachelcb80]

I have an Elos Mini that has been set up for a couple months now. Everything has been going fine up until this past weekend. We were gone from Friday through Monday night. When I got home Monday I noticed a couple of my zoa/paly colonies were looking unhappy (closed up or doing the umbrella thing). I tested my water and everything was normal except my salinity. It was at 1.029. Over the next several days I swapped out tank water for fresh water to bring the specific gravity back down. Two days ago it was at 1.026. Today it's back at 1.028. I have an ATO system, the water level is not changing in the sump and I haven't added any new water to the tank other than the fresh water changes this week. How can my salinity be changing so much?

I'm using a refractometer and will admit to using RO/DI water to calibrate it. But even if it was slightly off calibration wise, it's still registering a change in the specific gravity. Do refractometers go bad? This one hasn't suffered any damage.

I'm new to nano keeping (had a 125 gallon tank up until recently) so the rate at which things can change in this small of a tank is something I'm still getting used to. It doesn't seem like this is a normal flucuation though. Any ideas, help or suggestions would be appreciated!

[ReefingMadness]

Do you maybe have your ATO line in the tank water? If so, it may be that it is siphoning back into your ATO reservoir.

[rachelcb80]

Well I didn't really think about that possibility. I just checked the ATO line and I don't think it was dipping down below the water surface in my sump (it's behind my skimmer and I can't quite see it) but it was close. I cut it just in case. That all being said though, I just checked my top off water with my refractometer and it showed 0 so I don't think that was problem.

[uhuru]

are you dosing anything? supplementing anything?

[rachelcb80]

I dose the DIY 2 part. I've been testing my Mg and thus far haven't needed to dose it, so just Ca and Alk is all that's going in at this point.

[uhuru]

DIY 2 part will increase the salinity of your system. In a nano tank with heavy dosing this can be the cause of your problem. What are your Ca and Alk parameters? How much is consumed per day (how much do you dose)? How often do you do water changes? What are the starting Ca and Alk parameters of your salt mix?

[rachelcb80]

Well I'm running my Alk and Ca on the low side right now. Alk is 8 and Ca is 380. I've been slowly trying to fine tune my dosing pump timing and see what works best for keeping my Ca and Alk up and keeps my pH in check as well. (My pH has run low ever since I set up my 125 gallon 3 years ago.)

I'm actually not certain how much I'm dosing each day. I started out with 30 mL but have increased the pump time so I'm not sure what I'm up to now.

I do a 2 gallon water change once a week but haven't been real regular with that the last few weeks. I'm not sure what the starting parameters are for my new saltwater but I use Reef Crystals and mix it to a specific gravity of 1.025.

[Agu]

I have found that salinity creeping up has been an issue with my nano tanks. I can't explain it, it just happens, and I just deal with it.

fwiw,

[rachelcb80]

Agu, how often do you check your salinity and what do you do to deal with it? Just do some fresh water changes? How quickly do you typically see your salinity rising? Like I'm seeing a 0.002 rise in a two day period. Is that normal sounding?

[Agu]

I'll normally check all four of my nanos with a refractometer before I start doing my weekly waterchanges. I target 1.025 and invariably at least one tank is .002 or .003 above that. So I just start a drip of plain ro/di water while getting setup and doing water changes on the other tanks. Sometimes I'll have to scoop out a cup of tank water just to have enough space for the ro/di.

If you're topping off .002 seems a bit high for two days. I've never used the two part additives but that could well be the reason as pointed out.

[uhuru]

To see if the dosing is the cause, simply don't dose anything for a couple of days and measure your salinity. Does it still increase the same?

I would think that 30mL is pretty high for a 20g tank unless it has a lot of sps and clams. . . I could be wrong.

You many want to check your Mg levels, low Mg makes it hard to maintain adequate Ca levels.

[rachelcb80]

I wouldn't say I have a lot of SPS. Just a couple large frags right now. A few LPS and a mussle/clam thing that one of my Ricordea came attached to. I kinda thought it seemed like I was adding a lot of the 2 part for my size tank but unless both my Alk and Ca test kits are bad, this is the amount that maintains my Alk and Ca on the lower end. I've been meaning to buy another test kit of both just to double check though.

It's been over a week since I last checked my Mg so I'll do that and see where I stand with that. It's been high (1600'ish) everytime I've checked it so far so I haven't added any Mg supplement yet.

As far as not dosing for a couple days, will that have any effect on my corals or is it a short enough time that it won't matter? I know for sure it will cause my pH to drop quite a bit. Should I worry about that?

[Blitzburggirl]

When you do a water change, do you perhaps top off slightly above your top off sensor? (I do it to compensate for salt escape via skimmer)

If you do, your tank will experience evaporation, with no replenishment until it evaporates below the sensor, then top off to the point of the sensor, but not where the water level was before. Does that make sense?

Also, some brands of top off have different levels of accuracy, perhaps yours has a wider range?

[motionless]

Blitzburggirl -

Thanks makes a lot of sense, I do exactly that (top off way above low-level sensor), and I have the exact same issue as rachelcb80 (+.002 rise). I dose ~15-20ml of calcium daily.

Rachelcb80-

I think skipping your 2-part for a few days should be ok. You should still check your alkalinity during that time though to make sure things aren't way off.

[uhuru]

Originally posted by Blitzburggirl
When you do a water change, do you perhaps top off slightly above your top off sensor? (I do it to compensate for salt escape via skimmer)

If you do, your tank will experience evaporation, with no replenishment until it evaporates below the sensor, then top off to the point of the sensor, but not where the water level was before. Does that make sense?

Also, some brands of top off have different levels of accuracy, perhaps yours has a wider range?

She said she hadn't changed the water for a few weeks though, besides actually adding FW to the system.

If the 2 part is causing the problem, I would look to make sure the test kits are working so you are not dosing too much. If it just turns out that your tank requires heavy dosing, I would also try skimming wet to help compensate for the added salinity. Since the skimmer is kinda small you might have to just change out a few cups of tank water for fresh RO/DI water throughout the week. To ensure ionic balance, you could incorporate NaCl free salt in your dosing if you wanted... especially if you are not doing weekly w/c's... or get a CA Rx instead.

[uhuru]

Originally posted by motionless
Rachelcb80-

I think skipping your 2-part for a few days should be ok. You should still check your alkalinity during that time though to make sure things aren't way off.

or switch to dosing kalk for a few days

[NanoReefWanabe]

how long do you age your new saltwater for? to me it sounds like you have undissolved salt in your water that releases once it is in the larger volume of your tank...if this has been going on for a while there is a chance you have built up undissolved salt in your sump or sand etc...

[rachelcb80]

I turned my two part off yesterday. I'm going to do a water change today (I measure exactly how much I take out and put that exact amount back in) and keep track of my parameters and see where they level out. I'm stuck at home for the next few days but I'll order some new test kits (my LFS doesn't sell any good ones anyways) and when they come in I can double check with them. I think I'll probably look at a different option for supplementing Ca and Alk when/if I need to. I just think something isn't working right for me with the 2 part. (It's probably operator error but doesn't hurt to try something else)

NanoReefWanabe, I mix up a 5 gallon bucket of new saltwater and that lasts about two and a half weeks, so it's sitting for that amount of time. I let it sit for at least 24 hours before I use it the first time.

[rachelcb80]

uhuru, do you have a link to the NaCl free salt you're talking about? I've never heard of such so I'm not certain what your refering to. I'll admit to being a little confused as to what salt free salt is. Is it just all the stuff in a salt mix, except the salt?

[uhuru]

You got it! When you dose CaCl2 and NaHCO3 you are adding Na and Cl without the other elements normally found in NSW. If you do regular weekly water changes it shouldn't be a problem, and this is the common method with 2 part.

Theoretically with the NaCl free salt (and full balling method) you could go longer without water changes and not have the ionic imbalance as may be seen with 2 part. The NaCl free salt is dosed daily just like the other supplements. This is what I have gathered from my reading. You can read more here:

http://glassbox-design.com/2008/the-...from-two-part/

In the past I have used 2 part on a high demand nano and I experienced rising salinity like you. I counteracted it by skimming wet, replacing tank water with FW when necessary, and making water changes with slightly hyposaline SW.