Want To Turn My 80 Litre Tank Into Brackish

[kanzaris]

Hi

I would like to turn my 80 liter Malawi Tank into a Brackish Tank for my chromides and knight gobies. I had
planned to empty the water and coral gravel out of my Malawi Tank replace the gravel with sand and refill the tank with water out of my existing Brackish Tank. What would happen to the existing bacteria in my filter as this is now being filled with salt water ?
Any advise???

Thanks

Sabby

 

[nmonks]

Your bacteria should be fine. If you take the SG to 1.003, that won't affect the bacteria at all, and your knights and chromides will be as happy as the proverbial pigs. Over the succeeding weeks you can adjust the salinity a little higher if you want, and my monitoring the nitrites, you can see if the bacteria are stressed or not, and act accordingly.

I'd mix the coral sand with the gravel, to be honest. Neither knights nor chromides need a very high pH; 7.5 will do fine. The salty water should take care of that, and all the coral sand will ne needed for is to add a bit of a safety net buffering-wise. In a brackish tank, you want something that looks like a river rather than the sea. River sand, a few patches of gravel, and some nice water-worn boulders would be just the thing. Add a few plants (perhaps Java ferns on bogwood for the zero-care option) and you're laughing.

Cheers,

Neale

 

[AMS]

Assuming that your SG is under 1.005 your bacteria will probably survive the change. It is really not scientifically proven whether bacteria in brackish tanks is truly a different kind of bacteria of just freshwater bacteria adapted to the salty conditions. One big problem with bacteria is temperature change. Try to get the temperature in the Malawi tank the same as the current brackish tank, that way the bacteria will have a better chance.

IMHO do not change the entire tank water at once. Gradually fill 15% or so every few days while adding some ammonia. This way to bacteria will ease into the change and wont take as long to cycle if the bacteria were to die in the complete water change. Monitor your stats frequently.

 

[kanzaris]

Your bacteria should be fine. If you take the SG to 1.003, that won't affect the bacteria at all, and your knights and chromides will be as happy as the proverbial pigs. Over the succeeding weeks you can adjust the salinity a little higher if you want, and my monitoring the nitrites, you can see if the bacteria are stressed or not, and act accordingly.

I'd mix the coral sand with the gravel, to be honest. Neither knights nor chromides need a very high pH; 7.5 will do fine. The salty water should take care of that, and all the coral sand will ne needed for is to add a bit of a safety net buffering-wise. In a brackish tank, you want something that looks like a river rather than the sea. River sand, a few patches of gravel, and some nice water-worn boulders would be just the thing. Add a few plants (perhaps Java ferns on bogwood for the zero-care option) and you're laughing.

Cheers,

Neale

Neale

How long after the change over can I add the fish ?
I was going to change the coral sand to sand as the chromides are a breeding pair and in my existing tank they dig big holes in the sand to keep the fry safe.

Thanks again

Sabby

 

[nmonks]

I've taken freshwater tanks to 1.003 straight away, fish included, without any problems. AMS is right to say that changes in salinity can affect the bacteria, but I think the cut-off point is somewhere above 1.003, possibly 1.005, but I suspect higher. So I assume (and have found) no real problems with adapting filter bacteria from freshwater to SG 1.003; ecologically, that's a trivial amount of salt, it's about one-seventh normal seawater. You could probably drink that, and be fine.

But, to be on the safe side, adapt the tank over a few hours, at least. That's what I would do. I do that converting a freshwater tank from hard water to soft, and would expect it to be a good idea generally.

Cycle the tank with ammonia if you want, but I think that's redundant. The bacteria will adjust to a new salinity very quickly (their physiology is very much simpler than something like a fish) and provided you don't do anything silly like overfeed your orange chromides, I'd put them in straight away. But that's me.

Alternatively, and this is perhaps a compromise between my view and AMS', put the chromides into hard, freshwater in the tank as it is. Then make a series of water changes over the next few days, taking the salinity up a "notch" on the SG scale at a time (1.000 to 1.001, etc.). Chromides will be fine in freshwater for months, let alone days. I wouldn't chance knight gobies though, they can be a bit funny about completely fresh water.

Cheers,

Neale

 

[AMS]

I wouldn't chance knight gobies though, they can be a bit funny about completely fresh water.

That was my thought a while back as well, but I quickly learned that in my own experience that was not the case. I currently keep a breeding pair of knight gobies in a 29 gallon freshwater tank and they are doing quite fine. When the pH was slightly acidic I ran into problems with ick, but when I added crushed coral to raise the pH they had yet to have problems with ick. Coincidence? Maybe, but thats why when I hear people asking if they can keep BBG's in freshwater (despite naturally inhabiting acidic freshwater) I say "yes" but it helps if it is alkaline.

 

[nmonks]

AMS --

Your observation accords with things I've heard, that knights can be kept in hard, alkaline water, just not acid. But I do think they're easier in brackish. Probably exactly the same with bumblebees, yes, they can be kept in fresh, but they're a bit easier in brackish.

A while back I read a book that reported on monos being kept just fine in freshwater, but at a high pH and hardness, the implication being that with euryhaline brackish water fish, pH and hardness were actually much more significant than salinity. It just so happens that brackish water happens to raise the pH and hardness.

Cheers,

Neale