Salt/brackish Mathematics Help

[star4]

I need this explaining for a complete numpty to brackish conditions please (nicely though)
 
I am contemplating setting up a tank for mudskippers. The basic tank set up, decor etc tank size I can do, but I am really not sure on making brackish water. However I would like to use sand, rock and wood, does this have any affect on brackish conditions.
 
I have read up you add x amount of salt/litre of water, but what happens when you do a water change? surely some salt is left behind so would you add less salt next water change? would this lead then to doing a fresh water change in y amount of changes later??
 
Obviously I am going to need a salinity tester, but how do you work out how much salt to add from readings for the water change?
 
Does tap water conditions play any part in adding salt? My tap water has a pH of 7 and is quite soft, my tanks usually stabalise at 6.5 - 6.8, would this affect brackish conditions?
 
Thanks in advance.
 
 

 

[Donya]

I haven't kept mud skippers, so someone else will have to offer more species-tailored advice. I've kept estuary-like setups with a specific gravity around 1.015-1.018 and low-salinity setups around 1.008; I'm not sure what mud skippers need, but there are some common factors in how to regulate salinity and such.
 
 
 

I have read up you add x amount of salt/litre of water

 
You'll want to use a hydrometer or refractometer to make sure it mixed to the right specific gravity, which acts as an indirect measure of salinity. Following the directions on the mix itself or a modified version to get a different salinity often only gets you in the ballpark.
 
 

surely some salt is left behind so would you add less salt next water change? would this lead then to doing a fresh water change in y amount of changes later??
 

 
When water evaporates, the salt doesn't go with it (except for salt crusts that can form around the edge of the tank, but these don't balance out the H2O lost to evaporation in most cases) Again, you need a hydrometer/refractometer to keep track of the specific gravity. If the evaporation rate is very slow then you can probably just compensate for it via a slightly lower salinity water added during a water change. Higher rates of evaporation can require adding freshwater to keep a stable salinity, since otherwise the salinity can creep out of the intended range.
 
 

Does tap water conditions play any part in adding salt? My tap water has a pH of 7 and is quite soft, my tanks usually stabalise at 6.5 - 6.8, would this affect brackish conditions?
 

 
Tap water can interact badly with salt mixes, although it's less of a problem at lower salt concentrations. I'm not sure exactly what conditions mud skippers require. If it's very low salinity then tap might be fine, but if it is closer to marine salinity (like 1.015 or 1.018sg) then RO would probably be better. One of the issues with salt mixes is that even a low KH in the tap can cause stuff to precipitate out or make the mix stubborn about dissolving when you need higher salinities, but this is less of an issue if you're adding less of the salt mix.

 

[star4]

Brilliant thanks I can delve further now

 

[iliveinazoo]

Mudskippers will do well above SG1.005. I keep my mudskipper tank at SG1.010 & I suspect that they would even do well up to marine conditions.

First I'll start by saying do not adjust the salinity in your tank by more than sg0.002 to prevent killing off your nitrifying bacteria. Calculating how much salt to add to your tank is fairly straight forward if you know the salinity of the water in your tank and that you are adding. If we assume that you are doing a 50% water change then:
A completely fresh tank (SG1.000) will need SG1.004 added to leave you with SG1.002
At SG1.002 you will need to add SG1.006 to get to SG1.004.

Salt, rocks and wood can affect your tank water, salt will harden it and make it more alkaline, wood will soften it and make it more acidic and rock can do many things depending on the type of rock, if it has metalic veins then avoid, if it has calcerous seams then it will harden your water and it could be inert and have no effect.