Salinity issues - Should I be concerned???

[unwired]

I've ordered a good refractometer but it's yet to arrive. Here in the house the main unit I'm using is an in-tank one by Red Sea. I remove it at least once or twice a week and give it a thorough cleaning b/c of algae buildup and bubbles. My second hydrometer gives even higher readings so I don't trust that at all right now. I have a urinary refractometer that my dad (the Dr.) hadn't used in ages and was using on our old reef tanks 15yrs back. I'm not 100% on the readings there either so I just bought a marine unit which I'm waiting on.

Here's the scoop:
I noticed yesterday that my in-tank hydrometer was going off the charts.
1.026 or higher. Now, the refractometer was much lower (almost always in the 1.013 range and was only slighty higher when my other unit way haywire - if I'm reading it right). BTW - my R/o water puts it at the bottom line (1.000). I haven't tried distilled though I should.

I changed the water last night to bring my intank back to about 1.020 or lower. (I only have a cleaner crew and serpent start so far so I'm not as overly concerned as I'd be if I bought some pygmy angels). I looked again this afternoon and the numbers seemed high so I dumped out about another gallon and put in a fresh batch of R/O water. A few hours go by and the numbers seem to be rising again.

So my questions:
What other than evaporation can cause salinity to rise?
Could it be the macro algae in the sump? I just don't know.

I've been going on the theory that lower salinity is less stressful than higher numbers so I've been watching everything carefully until my new (hopefully trustworthy) refractometer arrives. I nthe mean time, I'm open to any thoughts or suggestions the community might have so I can keep the critters I've got in there somewhat happy. So far, they seem unaffected.

In case I've forgotten any important details here's a quick run down:

System started roughly 3 weeeks ago.

Display tank: 9G - Live rock/Live sand & critters. 2x 32W PC lights.
Actinic active for about 14-16hrs and daylight (with actinic) for 12. - suggested by CurrentUSA.

Sump: 10G Live Sand/ Live Rock rubble. Macro - Grape Calupera and Chaeto. Reverse lighting schedule / 18W full spectrum PC light. Growing nicely actually.

One hint here, before I did yesterdays water change I had a TON of of tiny brown algae across the top of the main tank. I skimmed it all and did the water change. It has not returned yet. Also, the main tank has a fair amount of algae that the cleaning crew works on. Strangely there is almost NO algae in the sump.

Thanks.

 

[Trogdor]

The best thing that you can do at this point is to take a sample in to your LFS and see if they will test it for you. This way you can find the hydrometer/refractometer that is the most accurate and use that until your new one shows up.

There is a temperature compensation equation that must be used to find the actual salinity depending on the room temp and water temp. I'm not familiar with it because the refractometer that i use has auto-temperature compensation (as I assume your new one does too).

Evaporation is the main component that can increase your salinity but salt creep can be another big issue. If you have any splashing then you will probably suffer some salt creep. It's the residue that if left behind after salt water splashes on a dry surface. It leaves behind the salt and it starts to cake up if you have a large amount of splashing. Most of my forms on my cover for my lights and on the cords for my powerheads and heater. Just keep up with your top-off and test it weekly to see how much you are loosing. I'm lucky that I check my salinity more than once or twice per month now that i know how much it's using. Be sure to follow the calibration procedure and use RO water. I used distilled bottled water from the gas station and mine is right on. Hope that helps a bit.

 

[The Kapenta Kid]

I think the fluctuations in SG you are experiencing are instrumental errors. Algae will not affect things.
As far as I understand, the rationale for running low SG tanks is that it discourages fish parasites. Higher SG should not bother your critters.
If you have an instrument that is reading 1,000 with RO water (distilled or DI doesn't matter in this case) then you should accept that, and note the temperature of the water that gives you that reading.
A very rough guide is to add 0,0002 to the actual SG reading for every degree F the tank water is above the temp of the RO water which registered 1,000.
I'm sure urinary refractometers read other things rather than NaCl, urea perhaps, but it may be a good baseline in your situation.
Just don't piss in the tank :mrgreen: