Sg And Ppt

[Bloo]

This is probably a daft question, but I really have no knowledge on SG - and need to set up a small tank for my Amano Shrimp "zoes" (babies) to metamorphose. But all the reports and articles work in ppm and state I need to have a level of 35ppm.

So I went to my lfs today to buy some marine salt and something to measure ppm - only for them to tell me they only have instruments to measure in SG So how do I convert ? Or do I not need to ?

Help

Edit: oo, I just saw this post a few lines down. I take it I need something like this ??

Further edit: Just read through that trying to understand how the refractometer works. It says things like
" it only needs calibrating with RO water" - I don't understand
I was just going to add marine salt to my tapwater and get the levels up to 35ppm (Edit: realised this was meant to be ppt)

 

[SkiFletch]

Specific gravity differs from salinity (ppt) in that SG is temperature dependent. They are slightly different but related values.

Here is a quick converter for the two. Keep in mind, this likely assumes a temperature of around 75f since its a marine converter. I assume your amano shrimp would be happy with a similar temp so this converter should work just fine for you. Also for your application, I would think that a simple float hygrometer would be sufficient, you shouldn't need a refractometer

 

[Aquascaper]

Some refractometers have both readings on them

 

[SkiFletch]

Wait, just re-read your post, you said 35ppm not ppt... Thats outside the range of a specific gravity meter and I would think on the order of a few teaspoons for 10 gallons.

 

[nmonks]

Hello --

Measuring salinity (which is normally grammes of salt per litre) is difficult for aquarists, hence the reliance on specific gravity. This is a nuisance if you're relying on scientific resources where salinity is usually measured directly as g/l or ppt (parts per thousand).

Anyway, I have not yet seen a simple formula for converting between salinity and specific gravity, because in reality while salinity is constant for any given sample of water, specific gravity depends not only on the amount of salt in the water but also temperature annd atmospheric pressure. I've created a simple little program that makes approximate conversions between them (as well as with percentages of seawater). It's called Brack Calc and you can download it here:

http/homepage.mac.com/nmonks/software/software.html

For your purposes, 1,000 ppm is equal to 1 ppt and approximately equal to 1 g/l. So if your baby shrimps need a salinity of 15,000 ppm that is 15 ppt or about 15 g/l. According to Brack Calc, that's about 40% seawater or an SG of 1.010.

Cheers,

Neale

 

[Bloo]

) Sorry guys - somehow my eyes read ppm when it clearly states ppt - I've just never come across ppt, so must have blanked right over that one. So it's 35 ppt I'm trying to reach / calculate.

Thank you for all your information. The chap at the lfs said he could get me a really accurate sg meter for £10 - which means I don't have to spend nearly £30 on a refractomer if I use the nifty conversions

It's all a bit of an experiment at the moment, so I don't want to spend £100's on equipment for zoes that are the size or dust specks and it all goes horribly wrong and it's money down the drain. I've already had to buy and airpump and a heater for such a tiny tank (£35 for those two things alone!)
That said, I always like to use the best value & quality for money goods - so not just cheapest.

SkiFletch, yes my water is exactly at 75F.

Thanks again

 

[Aquascaper]

The chap at the lfs said he could get me a really accurate sg meter for £10 - which means I don't have to spend nearly £30 on a refractomer

I'd like to see the SG meter that's more accurate than a Refractometer (especially for £10!)

Got any links to websites for the product?

 

[Bloo]

He never said it was better than a refractometer - but he said it's dead accurate
Do I believe him ? He's usually a very trustworthy guy with spot on info as far as lfs people go.
Nope - no link I'm afraid, he just said he could order it in for me.

 

[Aquascaper]

There is three main pieces of equipment that can be used for measuring salt content in water:

Swing-Arm - £5 (Rubbish)
Hydrometer - £10 (Ok but very temperature dependant)
Refractometer - £30 (Most accurate and not temperature dependant)

(rough prices of course)
Admittedly there could be something else that's used for measuring very small concentrations but I would be dubious. Best thing to do would be to either ask for more details so you can shop around/check on the internet or at least make sure that your not comitted to buying the item just because he's ordered it in.

I would be very surprised if there's one person on this whole forum who hasn't been fleeced by an LFS at some point in their life so just take their advice with a pinch of salt until you've checked it out for yourself

 

[Navarre]

If you truely want to have an accurate reading that is going tobe consistant then you need a refractometer. They measure in PPT (mine does ) and you should be aiming for 35ppt. You would be amazed just how far out the other 2 methods of SG/PPT are.

 

[nmonks]

Assuming these are brackish water invertebrates, then accuracy is irrelevant. All brackish water animals can easily handle fluctuations within that sort of range. They have to. So whether you use a swing-arm hydrometer or a refractometer is neither here nor there. Use the one that suits your needs and budget.

With corals you need consistency, because the SG/salinity of the sea is essentially constant. But in estuaries and salt marshes, the SG goes up and down all the time. There is actually some good evidence that variying the salinity is beneficial with brackish water fish, and I'd imagine the same was true for invertebrates.

The problem with raising juvenile crustaceans is almost never water chemistry, but food.

Cheers,

Neale

 

[Navarre]

I agree with that statement. The SG is not really an issue to behonest. Finding a suitable food is practically impossible (which is why there is very little success in breeding marines ).

 

[SkiFletch]

Assuming these are brackish water invertebrates, then accuracy is irrelevant. All brackish water animals can easily handle fluctuations within that sort of range. They have to. So whether you use a swing-arm hydrometer or a refractometer is neither here nor there. Use the one that suits your needs and budget.

With corals you need consistency, because the SG/salinity of the sea is essentially constant. But in estuaries and salt marshes, the SG goes up and down all the time. There is actually some good evidence that variying the salinity is beneficial with brackish water fish, and I'd imagine the same was true for invertebrates.

The problem with raising juvenile crustaceans is almost never water chemistry, but food.

Cheers,

Neale

Amen to that

 

[nmonks]

Which is exactly why so many marine fishes breed in brackish water. Even in the real world, it's difficult for juvenile marine fish to find food. So lots of them go inshore and breed in mangroves and other estuarine and brackish water habitats.

We often think of brackish tanks as a subset of freshwater aquaria, but really brackish water habitats are part of the marine ecosystem.

Cheers,

Neale

I agree with that statement. The SG is not really an issue to behonest. Finding a suitable food is practically impossible (which is why there is very little success in breeding marines ).

 

[Bloo]

Thanks again

This is what is said about food for them - so it doesn't "seem" to be that difficult ? :

The marine phytoplankton I use is by far the most convenient way to feed the larvae, in terms of yield and water pollution : I put the emphasis on this particular point because, after putting the larvae in the salt water tank, all I have to do is watch them grow with my arms crossed.

A few times a day, I use a spoon to slowly stir the water, thus mixing up particles of all sizes, formed of congregated algae, that accumulate on the bottom. I clearly see the larger zoes grab some of the particles to feed on them. This clearly illustrates that the phytoplankton is able to provide food to the smallest as well as to the biggest larvae.

You can try any other way of feeding them : it may work, but it will be much less convenient (you'll have to uncross your arms!), and will eventually produce a less satisfactory result.

My phytoplankton is Dunalliela Salina, but I think any kind of marine phytoplankton suitable for artemia breeding will do (eg. Thallassiosera Pseudomonas).

From this section of the "Breeding Caridina Japonica" article. Others seem to be along similar lines.

Edit: just realised this article does speak of ppm and not ppt.....

Assuming these are brackish water invertebrates

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 ?