Sg And Ppt

[nmonks]

Well, I'd heard the reverse, that in the wild these things inhabited (admittedly low salinity) salt marshes and swamps, rather than regular freshwater. I'd suggest doing a Google search using their Latin name (Caridina japonica) to dig up some scientific papers rather thah hobbyist hear-say. My gut feeling though is that it probably doesn't matter with the adults, but rather the juveniles need at least moderately brackish water.

Cheers,

Neale

I was under the impression they weren't All the reports I have read clearly state that adults cannot live and survive in anything but fresh water. It's purely the early stages (first couple of months) that the zoes need salt water (at full marine strength). Thereafter they naturally move into fresh water again ?

 

[Bloo]

Thanks everyone for your great advice Aquascaper, I've decided to buy that refractometer from Dave - he said I should receive it by Friday

I figure I'm sure to have a marine tank at some point down the line anyway - so it's an investment

 

[Aquascaper]

Nice one!

FYI - My Hydrometer read an SG of 1.025 @ 26c, when I checked with my new Refractometer it was actually nearer 1.029

That shows how inaccurate Hydrometers can be

 

[nmonks]

Well, the hydrometer is accurate only at a specific temperature, and so when used at a different temperature, it cannot possibly be accurate. There is nothing intrinsically wrong with hydrometers, it's just mass production means that none of them are properly calibrated.

If you took a refractometer and didn't bother to calibrate it, it would be just as inaccuate. But since we calibrate a refactometer each and every time, refractometers *seem* more accurate.

Cheers,

Neale

FYI - My Hydrometer read an SG of 1.025 @ 26c, when I checked with my new Refractometer it was actually nearer 1.029
That shows how inaccurate Hydrometers can be

 

[Aquascaper]

I was just pointing out the fact that Refractometers are not temperature dependant (as already covered in this thread) and therefore more accurate whilst also stating the level of inaccuracy....thanks for jumping in with the same info though

 

[nmonks]

Actually no, not the same info. What I was saying was that a refractometer is just as inaccurate as a hydrometer if it isn't calibrated. The idea hydrometers are *by definition* less accurate than refractometers is very misleading.

Cheers,

Neale

thanks for jumping in with the same info though

 

[Aquascaper]

Hydrometers are in no way as accurate as a Refractometer for measuring SG levels due to the fact that the temperature in your freshly mixed saltwater has to be at exactly the same temperature as your tank water to get an accurate reading to compare the two and ensure that you are adding water with the same SG.

By using a Refractometer temperature is taken out of the equation and therefore makes results more accurate.

If the person owns a Refractometer they will know how to calibrate it and if they use it without calibrating it then, frankly, they're idiots

The simple fact that a Refractometer can be calibrated by the consumer means that it is inherently more accurate than a piece of equipment that can not, ie. a Hydrometer or Swing Arm

 

[nmonks]

I agree that a refractometer allows the (hobbyist) user to take more accurate estimates of specific gravity; what one has to be careful about saying is that because we don't calibrate swing-arm hydrometers, that makes them less accurate devices. It doesn't.

If I had a swing arm hydrometer calibrated for use at 25 C and under 1 atm. of pressure, and my water sample was at 25 C and the ambient air pressure was 1 atm., then that hydrometer would be plenty accurate enough for most home-user purposes.

The problem is that the hydrometer one buys from Instant Ocean doesn't come with instructions telling the user what temperature and air pressure it's calibrated for.

I guess I'm arguing with you use of the word "inherent". To me, "inherent" means that the thing cannot, under any circumstances, do a certain thing. A swing-arm hydrometer can be accurate, if you know what it has been calibrated to work at. The fact that you don't, makes it *practically* less accurate than a refractometer, but not *inherently* less accurate.

Besides, I'm coming to this as a brackish water aquarist. Refractometers are currently the cat's pyjamas among some brackish water aquarists, though for the life of me, I cannot see why. Sub-10% accuracy in estimating salinity is probably useful for *reef aquarists* but it is totally pointless for any euryhaline, brackish water fish that not only expect variable salinity but positively thrive in it.

Cheers,

Neale

The simple fact that a Refractometer can be calibrated by the consumer means that it is inherently more accurate than a piece of equipment that can not, ie. a Hydrometer or Swing Arm

 

[Aquascaper]

If you're only bothered about SG being accurate to 'x', give or take 10% then you're going to kill a lot of livestock.

What you're saying is that as long as you are happy with a discrepancy between the tank SG and the SG of the water you're mixing of anything up to 20% then Hydrometers are fine for you to use - and you still maintain that they can be described as accurate.

I would describe them as inaccurate as they are totally dependant on temperature.

 

[Navarre]

The problem with other forms of measurement such as swing arms etc is that they are consistantly innacurrate. This doesnt mean they are wildly random or anything but are rarely true to the real salt content in the water. For example... My old swing arm used to read 1.025 and I would use this measurement each and every time i did a water change. However i later found that the true reading was over 1.030. Ok the level os contant was consistant but its true accuracy was far out. I was in the beleif that i had a tank operating at 1.025 yet it was operating at 1.030 or higher. For me this was not something i am happy to live with as fish have enormous strains placed on their internal organs, I felt they were safe yet i had them in very stressful conditions.

Another problem with swing arm especially are things like tiny micro bubbles formingonthe arm, salt creep (even if only a tiny amount) can also effect the reading wildly. Ok you can argue that you should maintain the hydrometer properly to gain the correct reading and this is probably true but when it comes to peace of mind i would not risk my tank or its livestock with anything other than a refractometer.

 

[nmonks]

Your quote here is out of context -- I said with euryhaline, brackish water fish a 10% margin of error doesn't matter. I then went on to say that with reef animals then you do need accuracy better than 10%.

I'm not recommending that anyone chuck out a refractometer and buy a cheap hydrometer instead. That would obviously be silly. But what is equally true is that for brackish water fishes -- and for that matter brackish water inverts like Amano shrimps -- then accuracy is far less significant. For example, the only person I know who has spawned Monodactylus argenteus in the last few years has been maintaining them at the wrong salinity, indeed, in a freshwater, not marine or brackish aquarium. Brackish water livestock not only tolerate but expect variations in salinity, hence my comments were specific to brackish water, not reef, fishkeeping.

(There's nothing to stop an aquarist using a refractometer in a brackish water aquarium, it's just not going to make any difference in terms of the health of the fishes.)

Cheers,

Neale

If you're only bothered about SG being accurate to 'x', give or take 10% then you're going to kill a lot of livestock.

 

[Aquascaper]

Your quote here is out of context -- I said with euryhaline, brackish water fish a 10% margin of error doesn't matter. I then went on to say that with reef animals then you do need accuracy better than 10%.

This is the marine section, not the brackish section, therefore my quotes are all in context

I'm not recommending that anyone chuck out a refractometer and buy a cheap hydrometer instead. That would obviously be silly. But what is equally true is that for brackish water fishes -- and for that matter brackish water inverts like Amano shrimps -- then accuracy is far less significant. For example, the only person I know who has spawned Monodactylus argenteus in the last few years has been maintaining them at the wrong salinity, indeed, in a freshwater, not marine or brackish aquarium. Brackish water livestock not only tolerate but expect variations in salinity, hence my comments were specific to brackish water, not reef, fishkeeping.

Again, this is the marine section not the brackish section

(There's nothing to stop an aquarist using a refractometer in a brackish water aquarium, it's just not going to make any difference in terms of the health of the fishes.)

There seems to be a theme here, this is not the brackish forum. It is of no relevance to know that you can afford a 20% margin of error on your SG levels in a brackish tank. This is the Marine section where margins of error like that cause unecessary deaths to fish and inverts. The advice given in this section is in direct relation to marine fishkeeping and as the original question was in relation to accurately reading SG and/or ppt the advice given was that a Refractometer is the most accurate and easiest way to check those levels for the hobbyist.

Thanks for the link to promote your little program but probably would have been better to PM the poster rather than start a whole issue over something with no relevance in the marine hobby.

 

[Bloo]

Sorry if I stared what this has become

I stared this topic here (and specifically not in the brackish section) because of the concentration level of salt require in the tank I'm setting up - which I believe/understand is at marine strength and not brackish - please correct me if I'm wrong. This is all new to me.

Neale very kindly replied because I asked him to (in a pm) when I started the topic (even though we have never corresponded before) - because he replied to one of my other topics on Amano Shrimp and I thought he might have some insight; and I would have liked to see his response.

I nonetheless appreciate all your replies and I've certainly learnt many new things

 

[nmonks]

Bloozoo --

Thanks for this clarification. I don't post brackish water stuff in a marine forum, but in this case, a question about Amano shrimps (which breed either in brackish and/or marine water, depending on what you read) I think my comments were relevant.

As I said before, I'm not giving anyone advice about reef tanks or marine fish. I appreciate Aquascaper's point of view, and I certainly bow to his better knowledge as far as marine reef tanks go, and certainly don't mean to be rubbing anyone up the wrong way.

Aquascaper -- I think you'd also find it an eye-opener just how many "marine aquarium fish" actually inhabit brackish water either for part of their life cycle or on brief hunting excursions: damsels such as sergeant majors, dog-faced puffers, sharp-nosed puffers, many moray eels, emperor snappers, some of grunts and sweetlips, all the batfish, stripeys, a few seahorses, pipefish, and gobies, etc., etc.

From the perspective of marine biology, there really isn't a division between brackish and marine. I think we'd all agree that this complexity is what makes learning about fishes so interesting.

Cheers,

Neale

Neale very kindly replied because I asked him to (in a pm) when I started the topic (even though we have never corresponded before) - because he replied to one of my other topics on Amano Shrimp and I thought he might have some insight; and I would have liked to see his response.

 

[Aquascaper]

It's no eye-opener as I do actually spend quite a lot of time researching fish, corals, etc. to help fellow hobbyists as best I can.