Nitrate Nightmare

Question
Ok i have been having a nightmare trying to get my tank up and running. I set up tank about 3 month ago and everything was fine then i think i may have added too many fish at once and they started to die off and the water went merky soo i read online and figured i needed to start all over again, so i did keeping fish in spare tank. Now i have put them back in to main tank they were fine for a couple of weeks and now the water has gone back to the white merky colour so i bought a test kit for nitrate and discovered extremely high nitrate so i have put them into a spare tank again and now i dont know what too do...
I have bought a gravel hoover to see if that was the problem- no joy

I have treated all water for a couple of days before adding water (when doing water changes of 10-25%) as i live in city center -no joy

So i realy dont know what to do

the fish also keep darting around so i figured their must be some sort of pest so i went to shop and got treatment they recomended and used that and it worked.

I have a plectomus (something like that lol)
5 small molly
1 plato (not sure if thats its name lol but it is a small black and yellow thing)
siamese fighter
and two weird black upside down things that resemble a cat fish

Im not the sharpist nife in the draw so i cannot figure what gallon the tank is but seems to be bare with the fish so it carnt be too small
(ohh yeah i have too plants in too)


PLEASE HELP ASAP costing money too sort and fish keep dying  

Answer
Hi Daniel
Saw your question in our question pool.  Well, it's been a few weeks now since you posted your question, so what's the status of everything now?

First, lets figure out your tank size.  You'll need to measure the length, width, and height of the tank.  Here's a link, scroll to the bottom and pop in the length, width, and height in inches and it'll give you the gallons.  If you need litres, scroll back up to the top of the page, and there's a conversion for gallons to litres.

http://www.fishlore.com/ConversionCalculator.htm

5 mollies
1 most likely a platy from the color description, but maybe a pleco if it's got a sucker mouth on it.
1 betta(Siamese fighter)
and 2 probably upside down catfish

Next, read this link:

http://freshaquarium.about.com/cs/biologicalcycle/a/nitrogencycle.htm

All new tanks go through what's called the nitrogen cycle, or the cycle process.  Sounds like that's what's happening with yours.  Takes anywhere from 6-14 weeks on average for the cycle to complete.  Now, when you moved the fish out to the separate tank, you disrupted the cycle and actually stopped it because that beneficial bacteria that was growing in the tank needs to have a constant ammonia source(your fish through their waste)to survive.  Then, you added the fish back in, so the tank started to "cycle" again-which caused the white/murky looking water.  Now during this cycle process, ammonia and nitrites will spike.  Both of those are toxic to fish, and can kill them.  Nitrates really aren't as much of an issue in small amounts, but you want to keep those under 20 ppm ideally.  So, you need to have a test kit for ammonia, nitrites, and nitrates.  There's 2 kinds of test kits, a dipstick kind and a liquid dropper kind.  Get the liquid dropper kind-yes, they're a tad more money, but more accurate.

Get back to me and let me know what's going on, and I can give you better info. But read through those links, figure out your tank size(hopefully it's large enough), let me know what fish you have left(don't buy anymore just yet), and we'll go from there.

Christy