guppy and tetra

Question
hello, I wanted to know how many guppy and neon tetra i can keep in a 35ltr tank? will they get on and will the tetra fin nip the male guppy fancy tails? and finally how do i know when my guppy girlies are ready to give birth as i have 2 and they are both pregnant. i did have (2m and 2f) 4 but the 2 males must have has a big scrap and the other one died. Its tail was in shreads and it lost colour. my tank has been running for 5 weeks and i did everything i was supposed to do, water testing and treating befor adding fish. I did have 4 guppy, a betta and 2 mollies but all but the guppy have died due to an amonia spike, which hopefully i have sorted out now by doing a 50% water  chenge, gravel hovering and ammo lock. I would like to get more fish soon as the tank looks bare but i no i should prob wait a few weeks or at least untill the fry are born. is that right? thanks

Answer
First of all, you have to realize that guppies are happy with salt in their water (1 tablespoon per 3-5 gallons), and Tetra's are somewhat sensitive to salt.  So here is your first "obstacle".  I personally have Tetras in with Mollies and Platys and salt, and do not have a problem.  That's not to say that you won't though.  As most everything with fish, it all depends.  

As far as how many you can keep in your tank, try to stick to the 1" of FULL GROWN fish per gallon (or about 3.5 ltrs.) of water rule.  It doesn't work in all cases, but for the smaller fish it does.  Neon Tetras get to be about 1.25" (3 cm) and are best kept in groups of 6 or more as they are schooling fish, and guppies get to be about 2.5" max (large female), usually smaller.  You can calculate from here.  

As far as when your guppies will have their fry.....when they look like they are literally going to blow up, then they are ready.  A lot of times their vent area will get dark, and you can also see the gravid spot (the fry eyes). That bottom fin tends to darken too as time grows closer. Finally, the guppy will appear to "square off", meaning the bottom part of her stomach will look "square"ish", like a box.  This is the sure telltale way that you are very very near.  If you are going to put them in a breeding box or net, then would be the time to do it.  I try to get my fish in breeder boxes about 4 days before they have the fry. This way they have time to relax and de-stress prior to having the fry and you have less chance of miscarriage.

It sounds to me like the fish you lost was either in a fight like you said and lost color due to stress, OR perhaps he had tail and fin rot.  The best medicine for this is to keep your water in pristine condition, being diligent in weekly tank cleaning and partial water changes.

The reason you lost your other fish is more then likely because your tank was not properly cycled prior to putting all of those fish in and your bio load went into shock.  You should read up on cycling a tank properly and do this prior to getting more fish, so that you don't needlessly lose any more.  I'm going to give you 2 sites to check out.  One for fishless cycling and one for cycling with fish.  Please be sure that you try one of these methods so you can properly prepare your tank for the fish you wish to get.  Here are the links:  http://kokosgoldfish.com/tom01.html and http://www.aquariumpros.com/articles/fishcyclefw.shtml .  Check these out, I'm sure you'll find them interesting!

Good luck and if I can help you along the way, please write me back!    ;o)