Reef Discussion

[potatocouch]

Gold! thanks @Savage Henry

 

[NiCd]

Another test you can do, if you have a decent set of scales, is to get 35 grams of salt and add it to 1000 grams/mls of RO water and see how close to 1.026 it reads

I have done this a few times when having vast difference between meters and wanting to see which one is closest to being right.

 

[Savage Henry]

Dry your salt in the oven for a standard length of time beforehand so you know you are using the same amount of salt.

 

[NiCd]

Dry your salt in the oven for a standard length of time beforehand so you know you are using the same amount of salt.

Sorry forgot that step, SH is quiet right.

 

[macca_75]

I follow exactly this: have always had my refractometer read 1.029 for my NSW and I just keep an eye on my tank to ensure that it hasn't varied much from 1.029. Because I use tank lids, I do not have to replace water and my salinity does not vary much at all.

Lids don't affect salinity. Only water evaporates (salt remains) and if you have an ATO the change in salinity should be nothing. What can affect salinity is salt creep from splashing, etc.

 

[potatocouch]

Ok, since I don't have access to NSW for now ... so what has happened now is: I've asked my LFS to calibrate my new refractometer for me ... I got it from Reef Secrets so I hope I can trust on its quality better than the one from eBay ....

Anyway put that aside .. now the real question ...

His ATC refractometer is heavier than mine .. which is odd ... physical both look EXACTLY the same.

So he calibrated it and found that both started with 0 SG with the calibration fluid.

But when he tested his water, he found that his refractometer measures 1.025 whilst mine measures 1.027.

Isn't this odd?

And when I got back home, I tested my RODI water (0 tds) and found it to read > 1.000 ... is this odd?

So, if I ask him this weekend to set my refractometer just below 0 to accommodate that 0.002 difference, do you think this will solve the problem? logically it should (mathematically).

 

[NiCd]

You need to calibrate it off a solution closest to which you want a reference point.

If you use your refractometer for RO, calibrate it off a know 1.000 source. If you want to test the salinity in your tank, calibrate it off a saline reference solution that has a SG around 1.026.

 

[Savage Henry]

Lids don't affect salinity. Only water evaporates (salt remains) and if you have an ATO the change in salinity should be nothing. What can affect salinity is salt creep from splashing, etc.

I think that lids do affect salinity indirectly by preventing evaporation which leads directly to increased salinity.

I don't think salt creep would not affect salinity if the water containing the salt evaporates and is lost from the system along with the salt. However, if you were to collect that salt and place it back in the aquarium then you would raise salinity.

People sometimes blame lids for a lack of CO2 removal and hence an increase in acidity, but I would have thought that your skimmer would be much more effective at gas exchange than an open topped aquarium. Even more effective would be a skimmer that has an airline long enough to draw in air from outside a house rather than drawing in air from within the room the tank is located or worse still, drawing in air from within the cabinet.

 

[Savage Henry]

You need to calibrate it off a solution closest to which you want a reference point.

If you use your refractometer for RO, calibrate it off a know 1.000 source. If you want to test the salinity in your tank, calibrate it off a saline reference solution that has a SG around 1.026.

Not sure if this explains or adds to what NiCd says, but the refractometer might not be linear. I guess, mathematically, it doesn't have a straight gradient, but is probably curved if that makes sense?

Just do as NiCd says and have standard calibration solutions for each test point, i.e. 1.00 and 1.026 (if you want 1.026). It's will mean that each time you want to change from testing your RODI or your ASW you are going to have to recalibrate the refractometer.

My way is to calibrate at 1.00 using distilled water and measure my NSW without further calibrate. I get 1.029, which is apparently not accurate. However, that doesn't concern me as time and time again the NSW is always measuring 1.029 and I just keep it at that. If the refractometer measurement of my NSW was varying, then I would be concerned about my refractometer.

 

[macca_75]

I think that lids do affect salinity indirectly by preventing evaporation which leads directly to increased salinity.

If your ATO replaces the water lost to evaporation and you had no salt creep, how does your salinity change? (lid or no lid).

 

[NiCd]

Through dosing

 

[Savage Henry]

If your ATO replaces the water lost to evaporation and you had no salt creep, how does your salinity change? (lid or no lid).

Obviously if you have an ATO and water lost due to evaporation is replaced with new RODI then your salinity should not change.

 

[Savage Henry]

Through dosing

Another element to the complicated modern aquarium setup.

 

[NiCd]

I always find it funny that nobody checks their chloride to sulphide ratio, which makes up over 70% of salt component and gets really screwed up by supplements yet things like iron which is like .0000003% gets more attention.