Hydrometer question

[pgsasi]

HI,
I have used a CoraLife hydrometer all these days and bought salt water from my LFS. Since I started using Red Sea Coral Pro Salt recently and started making my own salt water I bought the Red Sea's hydrometer. Coralife hydrometer is showing my sg as 1.020 and RedSea hydrometer is showing 1.028. This is a huge difference.. Which one should I go with? I have used the Coralife one for almost 3.5 yrs now.. shld I go with the readings from the new one ? please advise.

Cheers / Sashi

[Ninong]

Hydrometers are notoriously unreliable. A refractometer is a much better way to measure salinity. Over here, a decent refractometer runs about $45.

[MyNameIsJoe]

Lots of them on ebay..

[pgsasi]

Thanks.. How about the digital ones? are they reliable ?

???????JUN?????/PH?????????/???????????PH-2771

[ToddTT]

Did your meter have any air bubbles stuck to the arm?


High rating, 94 reviews:

Marine Depot Aquarium Refractometer


When you adjust your salinity to the correct level, do it slowly, over the course of days or weeks. 1.020 is low. And 1.028 is obviously too high.

But if it really is 1.028, your fish have already adjusted to it (assuming they are currently healthy?), so lower it slowly.

[mlovelace]

Did your meter have any air bubbles stuck to the arm?


High rating, 94 reviews:

Marine Depot Aquarium Refractometer


When you adjust your salinity to the correct level, do it slowly, over the course of days or weeks. 1.020 is low. And 1.028 is obviously too high.

But if it really is 1.028, your fish have already adjusted to it (assuming they are currently healthy?), so lower it slowly.

Todd, I noticed some refractometers state to use RO/DI water solution to calibrate and others state do NOT? What is in the solutions they give you to calibrate? I have been thinking about purchasing one myself. I noticed BRS has one for 39.99 that comes with solution, but states do not use ro/di water.

It would be much easier for myself to use RO/DI water, since I have a unit at home.

Thank you, Mike

[Ninong]

Thanks.. How about the digital ones? are they reliable ?

???????JUN?????/PH?????????/???????????PH-2771

I'm not familiar with the newer digital refractometers but I would assume that they would be very accurate. Is this what you're talking about? That's a Hanna digital refractometer and it runs $200 over here. It looks VERY nice and Hanna instruments have a very good reputation.

I followed your link and looked at the pictures. Both pictures appear to be combination salinity-pH monitors with leads to probes. I guess the probes are extra? The top one is around 12,000 yen ($133) and the bottom one is around 20,000 yen ($222). If the probes are extra, then that will add to the price. And, as always with probes, you have to keep them clean and properly maintained. And, eventually, you have to replace the probes with new ones.

Actually what I was talking about was a plain optical refractometer like this. That one is $50 at Premium Aquatics. You can find similar ones for less than that on eBay. That's the kind that I used but I would certainly love to try one of those Hanna digital ones.

[Ninong]

Todd, I noticed some refractometers state to use RO/DI water solution to calibrate and others state do NOT? What is in the solutions they give you to calibrate? I have been thinking about purchasing one myself. I noticed BRS has one for 39.99 that comes with solution, but states do not use ro/di water.

It would be much easier for myself to use RO/DI water, since I have a unit at home.

Thank you, Mike

Mike,

All of the cheapy (meaning in the $50 range and not the hundreds of dollars-range) refractometers are salinity (aka brine) refractometers. They are not seawater refractometers. In other words, they are calibrated to measure a NaCl solution, not seawater. They come from the factory calibrated so that distilled water (or R.O./D.I. water) reads zero.

I have never seen any of these shipped with FREE calibration fluid. Usually they charge you a few dollars extra for the calibration fluid. The calibration fluid is a standard 35 ppt seawater calibration fluid. If you calibrate with that solution, then distilled water (or R.O./D.I. water) will no longer read zero but you have the advantage of not having to adjust the reading in your head every time you test your tankwater. Since these refractometers are really NaCl refractometers, then using them with the factory calibration (distilled water = 0) means that if your tankwater reads 35 ppt, you really have 33.3 ppt salinity. That's because a 35 ppt NaCl solution has the same refractive index as a 33.3 ppt seawater solution.

I found it a lot easier to just use distilled water to check my refractometer. If distilled water read zero, then I knew that a reading of 36.5 ppt on the refractometer's scale meant that I had exactly 35 ppt seawater salinity. That's because the refractive index of a 36.5 ppt NaCl solution is exactly the same as the refractive index of 35 ppt seawater.

In practice, my goal was to get a reading of 36 ppt on my refractometer, which means I kept my tank at 34.5 ppt seawater salinity.

Every time this topic comes up, it usually results in a whole bunch of new questions. This topic has been discussed previously in detail but I was unable to locate the previous thread using the search feature.

P.S. -- I found it a lot easier to simply use the refractometer the way it comes from the factory and make the necessary adjustment in my head, especially since a reading of 36 ppt on the refractometer was exactly where I wanted to be: 34.5 ppt seawater salinity. Zenya preferred to re-calibrate his refractometer using the standard 35 ppt seawater calibration fluid. One of the main reasons I didn't want to do that was because it's a lot easier to have distilled water or R.O./D.I. on hand than it is to have a standard solution on hand.

Here's another thing to remember: 35 ppt seawater salinity equals 1.0264 specific gravity. However, it makes no sense whatsoever to talk about specific gravity when what we are really interested in is salinity. A re-calibrated brine refractometer will read specific gravity a little on the low side. It will read 35 ppt seawater as 1.0261 SG instead of 1.0264 SG. However, we have no interest in specific gravity whatsoever. It's totally irrelevant. All we really want to know is the salinity of our tankwater.

P.P.S. -- I was just reading up on the product description for that Hanna digital refractometer that I linked above in Post #7 and it displays actual seawater salinity, not sodium chloride salinity. That's really nice! I really like that little instrument!

After a simple user calibration with distilled or deionized water, a seawater sample can be introduced into the sample well. Within seconds, the refractive index and temperature are measured and converted into one of 3 popular measurement units: Practical Salinity Units (PSU), Salinity in parts per thousand (ppt), or Specific Gravity (S.G. (20/20)). All conversion algorithms are based upon respected scientific publications using the physical properties of seawater (not sodium chloride).

[Ninong]

For all practical purposes (our purposes anyway), ppt and PSU are the same. However, for the extremely nerdy, here is the scientific definition of PSU (practical salinity units):

The Practical Salinity Scale defines salinity in terms of the conductivity ratio of a sample to that of a solution of 32.4356 g of KCl at 15°C in a 1 kg solution. A sample of seawater at 15°C with a conductivity equal to this KCl solution has a salinity of exactly 35 practical salinity units (psu).

In practice, salinity is determined from empirical relationships between temperature and the conductivity ratio of a sample to International Association for the Physical Sciences of the Ocean (IAPSO) Standard Seawater. Comparison of results with other laboratories requires all researchers to use the IAPSO Standard Seawater for calibration.

I found that definition online. By the way, you will usually find salinity expressed as S= in scientific literature instead of PSU. S= means salinity equals.

There are two different scientific calculation standards used to describe the salinity of seawater but the difference between the two is extremely small. For our purposes, we can consider PSU and S= to be the same. In fact, PSU is often expressed as S= even though some people use PSU only when referring to one calculation method and S= when referring to the other method.

I found this excruciatingly complex discussion of practical salinity calculations online and figured I would throw it in here just for laughs.

[mlovelace]

Thanks Ninong!

This was the one I was looking at on BRS. I don't see the name brand of it though. It is listed at 39.99 plus shipping cost.

Refractometer for reading salinity w/ Free Calibration fluid - English

[ToddTT]

Todd, I noticed some refractometers state to use RO/DI water solution to calibrate and others state do NOT? What is in the solutions they give you to calibrate? I have been thinking about purchasing one myself. I noticed BRS has one for 39.99 that comes with solution, but states do not use ro/di water.

It would be much easier for myself to use RO/DI water, since I have a unit at home.

Thank you, Mike

The manual for the Marine Depot model:

http://akamai.f3images.com/IMD/UserM.../MD2101%20.pdf

Uses distilled water.

[Ninong]

Thanks Ninong!

This was the one I was looking at on BRS. I don't see the name brand of it though. It is listed at 39.99 plus shipping cost.

Refractometer for reading salinity w/ Free Calibration fluid - English

It says it's an ATC (automatic temperature compensating) refractometer and that's important. Virtually all of them are ATC nowadays. I think they're all coming from China -- all of these $50 and under units -- but they all seem to perform quite well. No need to pay $100 for an American-made one, assuming there are any American-made ones anymore.

And it looks like they're throwing in the calibration fluid for free. Some places charge anywhere from $2.99 to $9.99 extra for calibration fluid. As I said earlier, you really don't need calibration fluid but some people (e.g. zhenya) prefer to calibrate their refractometers using a standard 35 PSU calibration fluid. After you do that, distilled water will no longer read zero. Tankwater that reads 35 ppt on your re-calibrated refractometer will be an actual 35 ppt. Tankwater that reads anything other than 35 ppt will not be exactly what the ppt scale says but it will be extremely close and nothing you would have to adjust for.

Like I said earlier, if you didn't have a standard solution (35 PSU) to calibrate your refractomerter with, you could always just use distilled water or R.O./D.I. water and calibrate it so that that reads zero. In other words, pure freshwater would read zero and then 36.5 ppt on the scale would really be 35 PSU and 35 ppt on the scale would really be 33.3 PSU.

All of these ATC refractometers are coming from the factory calibrated with distilled water to read zero. I don't think any of them are coming calibrated so that a standard solution (35 PSU) actually reads 35 ppt. You have to re-calibrate it yourself using the standard solution.

[Ninong]

The manual for the Marine Depot model:

http://akamai.f3images.com/IMD/UserM.../MD2101%20.pdf

Uses distilled water.

Yes, that's a typical refractometer used in the hobby. They're all the same and they all work quite well. They all come from the factory calibrated with freshwater to read zero and they're all NaCl refractometers, NOT seawater refractometers. This is NOT a problem as long as you know what you have and how to adjust the readings. Or you can do like zhenya an re-calibrate your NaCl refractometer with a standard solution (35 PSU).

Note that the User Manual makes a big deal out of calibrating distilled water to read zero at an ambient room temperature of 68 degrees Fahrenheit. This is not really all that important as long as your ambient room temperature is somewhere close to 68 F, like say 74 F or 62 F. You don't want to calibrate it with an ambient room temperature of 45 F or 95 F.

From their manual:

Take the reading where the boundary line of blue and white cross the graduated scale. The scale will provide a direct reading of the concentration and specific gravity of salt (NaCl) in water.

Clean the prism carefully using a damp soft cloth. Do NOT immerse in water. Read warnings below carefully before use. Recalibrate occasionally.

Note that the User Manual is telling you that it is a NaCl refractometer and NOT a seawater refractometer. Seawater is not just NaCl in water.

Remember to clean off the glass surface with a damp soft cloth before and after using, especially after using. You don't want to get any build-up of salt on your glass surface that would affect your future readings.

[ToddTT]

Every time this topic comes up, it usually results in a whole bunch of new questions. This topic has been discussed previously in detail but I was unable to locate the previous thread using the search feature.

Probably somewhere in here:

refractometer site:reefland.com - Google Search

[pgsasi]

WOW... loads of replies... Thank you all.. I have ordered the digital Aquarium Salinity & PH Monitor 2 in 1
device. Will get it on Friday. Since this is for use in marine aquariums I think this will be my best choice. I had a good deal on this one.. paying 12,880 JPY.... Will let you all know how it works when I receive it.. And I should know which hydrometer is showing the right reading...

And the Red Sea Hydrometer is a submersible one and its inside my aquarium. There are no air bubbles..

Thank you all for sharing your knowledge..

Cheers / Sashi

[pgsasi]

All,
Apologies for the long delay... busy time @ work...

OK, I have set up the digiral PH/Salinity monitor and it works like a charm.... The readings are close to my Red Sea Hydrometer.. I am still on the little high scale and trying to slowly go down... SG right now is 1.025.. I am planning to maintain my tank @ 1.023.

Also, I am loosing atleast 3-4 L of water from my aquarium due to evaporation. I add about the same level of fresh water to my aquarium.. I am adding it at the rate of 4L in 40 mins... Is this rate OK or should it be slower ??? Please advise...

Cheers

[Ninong]

As long as you are using freshwater for evaporation replacement, it doesn't really matter how fast you add it ot your aquarium. Your evaporation is probably not more than two percent or so of the total water volume (unless you have a really small aquarium), so there is no need to take a long time adding the freshwater. I doubt that you will make much of a change in salinity.

It's only for people using limewater (Kalkwasser) as evaporation replacement that it is necessary to slow-drip the water.

By the way, why have you chosen such an unnatural salinity for your reef aquarium? Natural seawater salinity in the area of tropical coral reefs is 35 ppt (1.0264 SG).

P.S. -- What method are you using to maintain calcium and alkalinity?

How to Select a Calcium and Alkalinity Supplementation Scheme
http://www.advancedaquarist.com/issues/feb2003/chem.htm

[pgsasi]

Ninong,
I maintained my previous tank @ 1.023..My local aquarium shop suggested me this level.. if that is wrong. i will correct it.. Let me maintain the talk at 35 ppt.

I still consider myself new to reef aquarium.. I do not have any methods to maintain calcium and alkalinity...I change about 30L of water every week.... my tank capacity is 320L and sump capacity is around 35L... This is a fairly new tank....its just 67 days old...!! I have few fishes and mushroom corals..will slowly be adding more corals to the tank..

how long do you think I should wait before I add more corals ?

Regards / Sashi

[Ninong]

I would recommend that you not lower your salinity from its present 1.025 specific gravity. As far as calcium and alkalinity are concerned, read the following article and then be aware of the various choices. Once you have corals, you will need to decide how you're going to maintain your calcium and alkalinity because even doing water changes every other week won't be enough to keep up.

How to Select a Calcium and Alkalinity Supplementation Scheme
http://www.advancedaquarist.com/issues/feb2003/chem.htm

[pgsasi]

HI Ninong,
I have decided to start with Kalkwasser. (Even used calcium reactors are costing me about 30000 JPY/ 300 US.... expensive.. so will think about it down the line)...

As mentioned earlier, I use 4L of fresh water as my top off water... If I use my top off for adding calcium, how long should I take to drain 4L to my aquarium? also, please advise me if I have to add this to the return sump (from where water re-enters the tank) or the drain sump (entry point to the sump) {Apologies for my uncommon words.. .if they are... }

Should I add kalkwasser to my aquarium everyday through top-off or should it be once a week? (i guess the answer will be depends on the results of my calcium test??)... Please advise.

Also, I may have asked this question before.... but do you know of any shop that ships aquarium equipments to Japan? If none, do you know of anyone who can do that ? Lets say, if I can buy something online and ship it to this person and he can ship it to Japan ???

Cheers / Sashi