Hello people I have 120 liter tropical fish tank I have about 20 fish guppies male and female Molly's balloon Molly's and 2 plecs what other fish can I put in with them with lots of colour and all so I've had a few guppies that was pregnant but befor giving birth they died not really to sure why I have checked all water and all seem to be fine so not really to sure why they have died and how often do I have to do a water change I've had my tank set up for about 6 weeks can you helps out please thanks Russell