What's considered Brackish water?

[puffertt77]

Hey Guys

I know that full marine is between 1.020 and 1.025 but what is considered to be Brackish?

The reason I ask is that I've bought some river shrimp for my puffers and I want to keep them alive for as long as possible. The guy at the LFS said they need Brackish water and it must be cold. At the moment I've got them in the water they came in and I've put them in a 5 litre bottle that I've cut the top off.

I don't know if any of you saw my other thread stating that the river shrimp I bought before stayed alive longer in my Aquarium Salted FW tank than in my other normal FW tank that had no AS.

Ideally I'd like to keep them in my SW tank in a baby box floating at the top, I've got 2 in there now to see how long they survive

Dadof4 I seem to remember you mentioning keeping river shrimp alive, do you have any suggestions?

[Woland]

Brackish water goes from 1.001 to 1.018 (approx.)
The crossing-point beetween high-end brackish an marine conditions seems to be a matter of dispute.

[puffertt77]

Brackish water goes from 1.001 to 1.018 (approx.)
The crossing-point beetween high-end brackish an marine conditions seems to be a matter of dispute.

Thanks mate

[nmonks]

Brackish water goes from 1.001 to 1.018 (approx.)
The crossing-point beetween high-end brackish an marine conditions seems to be a matter of dispute.

I'd expand this a little.

For our practical purposes, brackish falls into two ranges, the "low end" where you'd keep plants as well as essentially salt-tolerant freshwater fish, and the "high end" where you'd be more interested in migratory or estuarine fish (and potentially invertebrates).

At the low end, anything between SG 1.002 to 1.005 (at 25 C*) will do fine. Whether you're keeping figure-8s, glassfish, bumblebee gobies, brackish water killis, livebearers, catfish, etc., all will do well across this range. So you're free to set the salinity as determined by the weak link in the system, usually the plants, most of which only thrive at around SG 1.003.

The high end is around SG 1.008 to 1.012 at 25 C, about 40-50% seawater salinity. Again, the precise value couldn't matter less, so you'd set it according to the weak link here. If you had a skimmer for example, you'd want SG 1.010 because that's about where skimmers start to earn their keep. But if a low salinity meant you could do more water changes within your budget, then that would be fine. Your scats, monos, green spotted puffers, mudskippers, violet gobies, Colombian sharks, etc couldn't care less.

The cut-off between brackish and what's called "saline water" is defined at 30 mg/l salinity, about SG 1.021 at 25 C. Normal marine water is 35 g/l, about SG 1.025 at 25 C. Hence old school marine fishkeepers who maintained their fish-only systems at SG 1.018 were keeping their damsels, lionfish, etc in brackish water! Strange but true.

Cheers, Neale

* Temperature is important; at 25 C SG 1.005 is 25% seawater salinity, while at 30 C it's 30% seawater, and only 21% seawater at 20 C.

[puffertt77]

Brackish water goes from 1.001 to 1.018 (approx.)
The crossing-point beetween high-end brackish an marine conditions seems to be a matter of dispute.

I'd expand this a little.

For our practical purposes, brackish falls into two ranges, the "low end" where you'd keep plants as well as essentially salt-tolerant freshwater fish, and the "high end" where you'd be more interested in migratory or estuarine fish (and potentially invertebrates).

At the low end, anything between SG 1.002 to 1.005 (at 25 C*) will do fine. Whether you're keeping figure-8s, glassfish, bumblebee gobies, brackish water killis, livebearers, catfish, etc., all will do well across this range. So you're free to set the salinity as determined by the weak link in the system, usually the plants, most of which only thrive at around SG 1.003.

The high end is around SG 1.008 to 1.012 at 25 C, about 40-50% seawater salinity. Again, the precise value couldn't matter less, so you'd set it according to the weak link here. If you had a skimmer for example, you'd want SG 1.010 because that's about where skimmers start to earn their keep. But if a low salinity meant you could do more water changes within your budget, then that would be fine. Your scats, monos, green spotted puffers, mudskippers, violet gobies, Colombian sharks, etc couldn't care less.

The cut-off between brackish and what's called "saline water" is defined at 30 mg/l salinity, about SG 1.021 at 25 C. Normal marine water is 35 g/l, about SG 1.025 at 25 C. Hence old school marine fishkeepers who maintained their fish-only systems at SG 1.018 were keeping their damsels, lionfish, etc in brackish water! Strange but true.

Cheers, Neale

* Temperature is important; at 25 C SG 1.005 is 25% seawater salinity, while at 30 C it's 30% seawater, and only 21% seawater at 20 C.

Thanks Neale

Very intresting, you've made me understand it very well

[Woland]

Brackish water goes from 1.001 to 1.018 (approx.)
The crossing-point beetween high-end brackish an marine conditions seems to be a matter of dispute.

I'd expand this a little.

For our practical purposes, brackish falls into two ranges, the "low end" where you'd keep plants as well as essentially salt-tolerant freshwater fish, and the "high end" where you'd be more interested in migratory or estuarine fish (and potentially invertebrates).

At the low end, anything between SG 1.002 to 1.005 (at 25 C*) will do fine. Whether you're keeping figure-8s, glassfish, bumblebee gobies, brackish water killis, livebearers, catfish, etc., all will do well across this range. So you're free to set the salinity as determined by the weak link in the system, usually the plants, most of which only thrive at around SG 1.003.

The high end is around SG 1.008 to 1.012 at 25 C, about 40-50% seawater salinity. Again, the precise value couldn't matter less, so you'd set it according to the weak link here. If you had a skimmer for example, you'd want SG 1.010 because that's about where skimmers start to earn their keep. But if a low salinity meant you could do more water changes within your budget, then that would be fine. Your scats, monos, green spotted puffers, mudskippers, violet gobies, Colombian sharks, etc couldn't care less.

The cut-off between brackish and what's called "saline water" is defined at 30 mg/l salinity, about SG 1.021 at 25 C. Normal marine water is 35 g/l, about SG 1.025 at 25 C. Hence old school marine fishkeepers who maintained their fish-only systems at SG 1.018 were keeping their damsels, lionfish, etc in brackish water! Strange but true.

Cheers, Neale

* Temperature is important; at 25 C SG 1.005 is 25% seawater salinity, while at 30 C it's 30% seawater, and only 21% seawater at 20 C.

Interesting stuff Neale.

I seem to remember reading that a skimmer would be absolutely necessary at 1.018.
Opinion?

[edmlfc1]

I always thought a skimmer would be useless at a lower sg. (below 1.018)
Does it work the same as in full marine?

[nmonks]

Skimmers can work at any salinity, and there are indeed freshwater skimmers designed for ponds. Skimmers merely replicate the mixing of air and water that happens all over the place, e.g., that foam that sometimes comes off algae-rich lakes and reservoirs.

However, it is true that *marine* skimmers may not work at low salinities. The cut-off point varies, but my experience and that of other aquarists I've spoken to is that a tall, powerful skimmer can work down to SG 1.010.

Cheers, Neale

[By_a_coo]

* Temperature is important; at 25 C SG 1.005 is 25% seawater salinity, while at 30 C it's 30% seawater, and only 21% seawater at 20 C.

Neale, I'm very glad you mentioned the importance of temperature on the density of water. Every place I read "some fish needs 1.005 or 1.012", or "keep your plants under 1.005"... those values mean nothing to me (to the fish and to the plants), since nobody mentioned the temperature wich makes a huge difference in salinity reading. Salinity is what we really want to know. I thank you very much to teach me the lesson.

[nmonks]

If you look at my Brack Calc application, it has a temperature slider along with the specific gravity slider. While the maths involved simplify things a bit, you can quickly get the idea of how temperature affects specific gravity.

So far as I know, all the commercially available aquarium hydrometers are calibrated for 25 C. I'm sure one reason so many people believe hydrometers are inaccurate is that they use them at the wrong temperature. Americans in particular seem to keep their aquaria much warmer than they need to, often around 28-30 C. Freshly draw tap water will usually be much cooler than 25 C.

One way to use Brack Calc is to decide the SALINITY you want, set the TEMPERATURE of the bucket of water in front of you, and then move the SPECIFIC GRAVITY slider until you get the salinity you need. It may well be different to the SG 1.005 or whatever your book tells you, because the water is hotter or colder.

Do also note that air pressure is a factor as well. I ignored this for Brack Calc, but I guess it could make a difference if, for example, you lived at a very high altitude.

Cheers, Neale

[By_a_coo]

If you look at my Brack Calc application, it has a temperature slider along with the specific gravity slider. While the maths involved simplify things a bit, you can quickly get the idea of how temperature affects specific gravity.
One way to use Brack Calc is to decide the SALINITY you want, set the TEMPERATURE of the bucket of water in front of you, and then move the SPECIFIC GRAVITY slider until you get the salinity you need. It may well be different to the SG 1.005 or whatever your book tells you, because the water is hotter or colder.

I always use your software before any water changes. It's perfect! Your explanation on how to use your program is always useful. And I use it just the way you mentioned above. Thanks a lot Neale.