got a red clawed crab but how do i convert the tank to brackish?

[johnathonlove'sfish]

so i got a red clawed crab and i intended to change the tank to brackish but hydrometers dont go down to 0.002 which is what i intended on raising it every week so that my biological filter doesnt die off.can anybody tell me how many teaspoons or mililiters it takes to get 0.002? also how can i sex the crab other than turning it upside down? and how many males and females can i keep in a 20 gallon long? thanks!!!

[SLeen]

I'm not sure what you are trying to do with your filter. But honestly, crabs are not that sensitive to changes in salinity. I would just mix a batch of water with about 1.005 salinity. Then you can add more salt water gradually that has a higher sg.

red clawed crabs arent that easy to sex compared to fiddlers, but if you look at the claws on a female RCC, they are generally more slender and not as large.

I think, in a 20G, you could keep about 8 crabs. Maybe 2 males and 6 females.

[johnathonlove'sfish]

well the filter was seeded in freshwater so wouldn all of my beneficial bacteria get killed off? then id have to cycle the tank with my crab in it and id rather not do that. and could the claws be distinguished even as juveniles?

[SLeen]

It is harder to judge the sex when they are small. But if you are looking at them side-by-side, you can usually still tell a slight difference.

As far as your filter goes, yeah I suppose some of the BB might die off if you just drop it in brackish water with a high salinity. But a sg of 1.002-1.005 is still pretty fresh if you want to start with that. The reason hydrometers dont read below 1 is because those levels are still pretty much fresh water. People add aquarium salt to fresh aquariums for many different reason with no ill effect on the filter. I wouldnt worry too much about it.

[johnathonlove'sfish]

what im doing is adding about a quart and 1 half of the salinity i want 1.008. and ill do that once a week each week. i actually caught him today and put him in a little betta cup and looked underneath him and im almost 100% sure its a male. let me upload a pic just to make sure though. is having a male and female in a 10 gallon for a couple of weeks too much? can i keep a pair of fiddlers with a pair of red claws in a 20 gallon long?

[johnathonlove'sfish]

the first pic is of him in the tank, the second is him being sexed (so what do you think boy r girl?), and the third is of the tank but it looks a little different now.