is that 125 liters or gallons? Whats the filtration? A tank with bad filtration can be overstocked with far fewer fish then one with overdone filtration. And lat question, whats the measurements? Long, Tall, Deep type measurements.
If liters as i believe, then here are some things you should be warned of:
Betta(fighting fish), male or female, will fight, as their name suggests, among themselves and among other fish that look like betta (fancy guppies, long fined tetras, long fined anything really)
White Cloud Minnows need a colder tank the guppies and tetras, so you should put them in an entirely separate tank with other coldwater fish.
Guppies will breed, and are livebeares. If you do not already have babies you will within 2 months, and so many you cannot count them. Also, when you have both genders the best thing to do is have a male/female ratio of 1 male/2 females or more. If you do not you can have fighting between males. Females are fine in as large a group as the tank can safely support, as long as you are ready for the fry that will pour out of them.
Is that a bristlenose pleco? They need driftwood for food.
Here is what aquadvisor has to sat about it:
Note: Betta [Male] may jump - lids are recommended. They can become stressful under presence of too many shoaling species. Try to keep under 1 shoal if the tank is small. Individual bettas may exhibit varying degrees of aggression and care should be taken that exceptionally aggressive/territorial fish be separated from a community before any damage may occur.
Warning: Betta [Male] is not recommended to be with Betta [Female] - further research is highly recommended.
Warning: Betta [Male] is not recommended to be with Bristlenose Pleco - further research is highly recommended.
Warning: Betta [Male] will likely to fin nip Guppy.
Warning: Betta [Male] is not recommended to be with Guppy - further research is highly recommended.
Note: Betta [Female] can still become aggressive even if she doesn't show aggression right away. Not recommended to be mixed with peaceful community species. Also, they may jump - lids are recommended.
Warning: Betta [Female] is not recommended to be with Betta [Male] due to high male aggression.
Note: Bristlenose Pleco needs driftwood.
Warning: Guppy is not recommended to be with Betta [Male] - male betta may attack a male guppy by mistake thinking he is another male betta.
Recommended temperature range: 24 - 25 C.
Recommended pH range: 6 - 7.8.
Recommended hardness range: 5 - 15 dH.
Recommended water change schedule: 27% per week.
Your aquarium stocking level is 61%.
Here is a link:
http://aqadvisor.com/AqAdvisor.php?...AqSpeciesWindowSize=short&AqSearchMode=simple
Thats without a filter. Technically your tank is not overstocked, but you should do some major changes before adding anything to it. You want your fish to be safe and happy, right?
Betta/fighting fish: Separite tanks, each gets at least 5-10 gallon tanks.
Wight Clouds: Separite tank, colder water with other coldwater fish. Small.
Guppies: More females or males will fight. Or dump the females totally and get all males, then there will be no breeding or fighting.
Pleco: Get driftwood for it to eat.
Do those things and your fish will live long and healthy lives.