mysteriously decrasing salinity...

[tankedchemist]

So, I've done two 10% water changes this week, because I added a bunch of LR and got an ammonia spike. I'm using RODI to do it, and I let the salt mix at least 24hrs before changing the water. Here are my params:

NH3 0ppm (finally!)
pH 8.6-ish
KH 21 dKH
Ca 350ppm
NO3- 10ppm
sp grav 1.0205/salinity 28.5ppt

SO, the problem is, I've been seing a steady decrease in my salinity... I haven't had to add any water due to evaporation b/c I've been doing so much water changing, and whenever I change water, the new stuff is at about 1.024 sp. grav.... so what's the deal? Also, my pH is a bit on the high side and apparently rising, and KH is also high... what is going on??? I thought all these params were supposed to go the other direction... or is it opposite day and no one told me? :)

Thanks in advance!!

 

[Bifferwine]

Are you using a protein skimmer, and if so, is it running wet? A skimmer will pull salt water, but I can't see that making that much of a difference.

Also, how about salt creep on and around your tank and equipment? That's another way to lose salt.

Other than that...dunno! Are you using a hydrometer or refractometer to measure your specific gravity? If you're using a hydrometer, you could just be getting off readings, since they are known to not be that accurate. Invest in a refractometer instead, they run about $40 to $50 and you don't have to throw them out every 6 months like you do the hydrometers.

http://www.drsfostersmith.com/product/prod_display.cfm?pcatid=9957

And yes...your pH should be dropping. Weird.

 

[ccCapt]

What brand salt are you using? What brand alk test kit...because its impossible to have a reading of 21 dKH. A normal alk reading is around 8 dKH.

 

[tankedchemist]

I don't have a skimmer on it yet, and I don't see all that much salt outside the tank. There's a little bit, from when I drip water as I take my hands out of the tank.

I use a hydrometer, but I'll go see if I can get a refractometer from the LFS.

I use Instant Ocean salt, and an API alk test kit. The chart doesn't go up to 21, but it gives you the conversion amounts. Why do I have so much carbonate?!

I lost an invert this morning (coral banded shrimp) so I need to figure out how to fix this problem asap. thanks for the help

 

[AdeptMrSniffles]

Maybe when you do a water change just fill up with RODI. If your ALK is high then your PH is gonna be high, at least its that way with pools. Don't know a whole hell of a lot about Tank Chems so I don't know if that'd work. Just thought I'd throw it out there.

 

[tankedchemist]

Ok, I got a refractometer, and it turns out my salinity has been spot-on. not sure what's wrong with the hydrometer, but at least that's one mystery fixed.

As for the pH/KH issues, some time between last night and now, the problem has resolved itself. I don't know if my polyfilter pulled the kh out, or what, but it's all fine now... kh is a little low at 7, but I'll do another water change tomorrow to fix that.

weird!! Thanks for all the advice guys.

 

[Smitty]

I'm glad the problem is solved...Most hydrometers do give bad readings, so good thing you picked up a refractometer...You may also have a bad batch of salt, it has happened before...next time you make a new batch of saltwater...test it before adding it to the tank, or, it may be a bad test kit.

 

[Bifferwine]

Ok, I got a refractometer, and it turns out my salinity has been spot-on. not sure what's wrong with the hydrometer, but at least that's one mystery fixed.

I figured that would be the most probable answer. Hydrometers are not reliable.

 

[tankedchemist]

So, a question about the refractometer... it's scale is from 1.000 to 1.070 and it's a small scale, so it's hard to get precise readings in the range I want. Are they all like this? OR did I get the wrong one?

 

[yote]

Your refractometer should have another scale that shows parts per thousand.Mines got the salinity(ppt) on one side and specific gravity on the other.You'll have better luck with the PPT scale since the temperture dont effect it.Temp will effect the specific gravity a bit.
As for your parameter swing.Did you let the water mix overnight before doing the water change?

 

[daugherty]

temp can play a role you test it before it goes in at one temp than test again at a different temp and it will be different

 

[tankedchemist]

Yeah, I did-- though originally when I started the tank, I wasn't waiting before addng it to the tank... could water changes I did a month ago effect it now?