Currently in my livebearer tank I have 3 mollies, 3 platies, 2 swordtails and a BN pleco. I'll probably add guppies later this week, along with another female sword, just to complete my baby machi- err, livebearer community.

My plan was, once I rehome the BN to a new tank, to slowly convert the tank to a brackish water set-up. I was discussing this earlier with my LFS's owner, and he said that while mollies do fare better in BW tanks, that other livebearers won't.

Is this true? If it is, I must say I'm a bit dissapointed.

PS:
A question has been plaguing my mind lately. If the nitrifying bacteria are different in marine and freshwater set-ups, what kind are in a BW tank? If you have an answer, please share it.

I guess no one knows?

[quote name='TylerFerretLord' date='Oct 13 2007, 02:51 AM' post='1795299']
Currently in my livebearer tank I have 3 mollies, 3 platies, 2 swordtails and a BN pleco. I'll probably add guppies later this week, along with another female sword, just to complete my baby machi- err, livebearer community.

My plan was, once I rehome the BN to a new tank, to slowly convert the tank to a brackish water set-up. I was discussing this earlier with my LFS's owner, and he said that while mollies do fare better in BW tanks, that other livebearers won't.

Is this true? If it is, I must say I'm a bit dissapointed.



Why do you want to switch to brackish?

My mollies.

Mollies, while naturally found in brackish water, do not require brackish water. They are almost always acclimated to freshwater in stores. That being said, the salt in brackish water is supposed to neutralize some of the nitrates in the water, which Mollies seem to be more susceptible to than other fish, including other livebearers. The easiest way to deal with things is really to just leave the tank freshwater and to keep up with water changes to make sure your nitrates never climb over 20 PPM. I keep a freshwater tank with Mollies and other fish, no salt, and I keep my water levels clean. I have had no problems with the fish, including the Mollies.

Mollies DO fare better with the extra salt, and it's good for their health, so I really do recommend it. I think the salt is fine for most livebearers and can actually be quite beneficial. Other normal tropical fish might not like it as much, but I doubt it would do them much harm. Basically, I think if you add the salt all your fish should be fine.

Mollies do not require salt in their water. Many species are found in exclusively freshwater environments although the majority come from brackish waters and some from coastal areas. That said, those from your lfs do not live in brackish water and if they came from hatcheries where brackish water is used then they will be switching back and forth too much causing stress. That said, if you do decide to go brackish, your other livebearers will be fine so long as you dont just jack up the salt level right away. If slowly acclimated guppies can live in ocean water for extended periods. The brackish water will really only benefit you because it keeps down the level of harmful chemicals in your water which mollies are more sensitive to. This is the primary reason they do better in Brackish. As someone else said, regular h20 changes has the same effect.

Keep in mind that if you do start adding salt, you will need to remove water before adding new salt since the salt you add can only be removed with the water itself and does not evaporate or dissipate.

Here's the science: both mollies and guppies (including Endler guppies) can tolerate any level of salinity you want. Both can be acclimated to full strength seawater, and indeed have been acclimated to hypersaline conditions, that is, water that is *more* salty than seawater. In the case of mollies, to water more than twice as salty as the sea.

Platies and swordtails are different. They are not commonly found in brackish water and are best considered freshwater fish. However, both are found in brackish water in the wild, for example in Hawaii where they are found in waters up to SG 1.001. In aquaria, they are tolerant of brackish water up to at least SG 1.003, and perhaps slightly more if you're careful.

So, if you want to create a brackish water aquarium for the benefit of mollies (a good idea, even if not 100% essential) then the presence of other livebearers isn't normally a problem. SG 1.003 is adequate for mollies, and tolerated by all other livebearers if they are adjusted to the salt levels slowly. I'd suggest over a course of several weeks. Mollies can be dumped in freshwater from seawater, and vice versa, but the other livebearers need to acclimated much more carefully, especially platies and swordtails.



Salt DOES NOT keep down the levels of harmful chemicals. What it does is reduce the toxicity of nitrite and nitrate. The levels of both remains the same as before. But since mollies are especially sensitive to both of these, salt makes it easier to keep mollies in tanks with high levels of nitrite and nitrate than would otherwise be the case. Indeed, if you live somewhere that the water has high levels of nitrate (as here in Southern England, often 50 mg/l right out the tap) adding salt to the aquarium may be the *only* way you can keep mollies successfully and reliably in the long term.

Cheers, Neale

PS. Ancistrus sp. 3, if that's what you mean by a "bristlenose catfish", is fine up to SG 1.002. There are numerous truly salt-tolerant catfish and loaches on the market. Hypostomus plecostomus, Hoplosternum littorale and horseface loaches would all be fine with mollies at SG 1.003 or so. Hoplosternum littorale is actually very salt tolerant, and will easily take 1/3rd seawater.

This post has been edited by nmonks: Oct 20 2007, 11:58 AM

Thank you very much for that post, nmonks.