Tetras Bullying Each Other?

[Howard0]

So I've had my 10g tank for almost 2 weeks. Had my water tested and it appears to be fully cycled thanks to some filter sludge, old gravel and bacteria packets the store provided.
 
I had 3 Glowlights originally and added another 2. Four of them like to school together but there's this one little one who likes to hide. I caught two of the larger Glowlights chasing him around and bumping or nipping at him (couldn't really tell as they move kind of fast). He's about an inch and a quarter and the other two are two inches.
 
They're all eating and apart from the water being a bit harder than normal nothing's different. (I was told to do a partial water change to try and correct the water hardness) I've got them in a heavily planted tank heated to 78 degrees and a 90gph filter. The only other thing in there is a inch and a half ball of moss I'm convinced I overpaid for ($10).
 
Any ideas on why my tetras are picking on the little guy?

 

[BerryAttack]

the numbers should be a minimum of 6+ ... did you check  your water stats before adding fish? what about weekly water changes

 

[SarahR]

You can decrease water hardness by using distilled or RO water for part of a water change. How much depends on how much of a decrease you need. Generally fish adjust to whatever hardness and PH you have as long as it isn't extreme, changing them isn't often necessary.
As for why the one fish is being picked on, even with social fish it isn't unusual for larger ones to chase and dominate smaller members. Wild schools are large and there is plenty of room so aggression is spread around and no one fish is subjected to all the attention. A fish that wants to hide may be sick, and fish often try to drive sick ones away. Fish can get sick from being bullied, or be bullied because they're sick. It would be best to get it out of the tank, watch for any symptoms and treat if necessary. If it's just small but healthy you could see about trading it toward a couple of larger ones. I know quarantining can be difficult if you have just the one tank.
Your tank is pretty new. Make sure it's fully cycled and stable before adding too much or problems can snowball on you.

Marino balls are usually a bit of a letdown when you first get them, but if they grow well they are quite impressive and fascinating. Best of luck with the tank.

 

[Tim95]

Most shaoling fish tend to nip each other because they get bored, and since one is smaller then the rest it would make a great "toy" for them, try added 4 or 5 more and it should help with the bullying, though it will never disappear. It helps them to build a pecking order, but with more of them, it will help to disperse it over all the fish, instead of just one. If you can, get a couple smaller ones, of equal size to the small one being bullied now

 

[l_l_l]

tim95 gave great advice, although in a 10 gallon tank you should not put more than 8 of them.