Sexing baby mollies and keeping Nitrate levels in check

Question
I actually have two questions to ask here.

I have a typical community tank with a variety of breeds.  I have a female molly that gave birth to a fry of about 15 about a month ago.  Only two survived.  Once they grew big enough I began to try and figure out what gender they are.  I thought they were both female, but one of them is now chasing around one of my females like it's trying to mate, and the fins on the underbelly are now starting to look more like the male's.  Are all Mollies born female and then go through some sort of hormonal changes that determine the sex later on?  Just curious about this one.

Also, I've been having a tough time keeping the nitrate levels down in my tank.  I've been doing 25% water changes about once every two weeks, but that doesn't seem to be helping.  Is there a treatment that you would recommend?  
Thanks,
Amy

Answer
Hi Amy
That's an interesting question on the mollies.  I've never heard of that, but that doesn't mean anything lol.  I have heard of certain fish, saltwater parrot fish, some other one I can't think of, and I just found out guppies, can actually change their sex when they're young if one of the sexes isn't around.  I'll check into what you asked, and if I find out it's true, I'll send a follow up to you on it.

As for the nitrates, what size tank and how many fishes & what kind are in it?  Maybe it's overstocked?
I'm a big fan of doing water changes once a week.  I usually recommend 20-25%, but that really depends on how overstocked the tank is too.  If it's overstocked, should do a little more then that.  I'm not advocating overstocking a tank here, it's just a fact of life that people will do it, usually not on purpose lol.  Also, if you use tap water, try testing that for nitrates.  It's not uncommon for there to be high nitrates in the tap water.  If you have a test kit, just put some in a cup and test it like you do your tank.
 
There is a product out, it's made by Seachem called Prime.  It's a red and white bottle, I highly recommend it, and I know a lot of fish people that use it.  It detoxifies nitrates and such.  You use it with your regular water changes to treat the water/remove the chlorine & chloramines.  I still say find out what the source is for the high nitrates though.  The big bottle is kinda expensive, but it's good for I think 2500 gallons, so it lasts a looooong time.  Here's a link where I'll buy it from sometimes and you can read about it, this is actuallly really cheap for it, but you'll have to pay for shipping.  I'll usually buy stuff here and buy a few things to make the shipping worthwhile.  I think the petstores sell it for around 10-11.00 for the big bottle.

http://www.drsfostersmith.com/Product/Prod_Display.cfm?pcatid=4057&Ntt=prime&Ntk...

Hope that helps and good luck!!

Christy

FOLLOW UP:
Hi again
I found a kinda interesting forum question, regarding swordtails changing their sex.  Some are claiming it's just a myth that livebearers will change their sex, but like I said I read somewhere else that they do.  So another one of those situations where everyone has their own opinion.  I've never noticed, so I can't say either way which I believe lol.  Here's that link, not sure if you'll have to sign up at the forum, it is a good fish/aquarium forum, so I'd recommend signing up anyway.  If you don't and aren't able to view the article, here's a copy/paste and to give credit, it's on the Aquarium Central forum, and the question was mainly regarding swordtails(another type of livebearer similar to platys:

"its anal fin is pointed like a males and i read somewere that in some cases the under go a sex change and it was a pritty big female so i dont think its devloping late

What you read was outdated. Usually in these cases the fish are born with the internal sex organs of a male. You should note that fry all look female with a triangular shaped anal fin and not a gonadopodium. Not all swordtails will mature at the same apce, as I stated earlier and some will even develop their "sword" a year after they are born. Swordtails do not change sex. A lot of reef fish do, but swordtails are not marine, don't live on reefs and again, do not change sex spontaneously."

Guess that kinda makes sense.  I know certain animals will change sex, like that lizard in the news recently.  Hope that answers your question!!

Forgot to put the link in.....

http://www.aquariacentral.com/forums/printthread.php?t=47136

Christy