Question About New Fish Tank And Fish-Less Cycle

[FilipeB]

Hello again guys!
 
We've just put some fish into the tank today. It's so amazing to see ^^ I didn't really make an inventory, but it's only a handfull of mollies, neons, guppies and 2 clown leaches (to deal with snails) and 3 yamato shrimps (I just love them, they look awesome

).
 
I did however think I messed something up. I didn't realise I was meant to add declorinathor to the water BEFORE I changed the water in the tank. I'm afraid I might have killed my bacteria

I will do some ammonia testing first thing tomorrow morning.
 
I also found something unexpected. At first it looked like a bit from a plant, but them I noticed it looked like an animal, and then I was sure when it moved. I've managed to identify it as a Damselfly larva. Last I saw it, it went inside my filter. Not quite sure what to do now, as I read that they are predatory

It was quite a beautiful looking insect, but if it's going to harm my fish tank, I need to get rid of it, but I don't know how.
 
Some pictures:

 

 

 

 

 

 

 
 
Also, 3 little videos I took of him:
View My Video
View My Video
View My Video

 

[FilipeB]

So I just went to check my tank now, and I can see 3 dead fish. One molly, one guppy and one fish which I can't remember the name (small one, like the neons). Everything is normal. PH is between 8 and 9, same reading as I got yesterday. Ammonia is 0 and nitrites are 0. I don't know why the fish have died

We even bought something yesterday called "health guard" from the brand "i love fish" which is a treatment to use when you put in new fish. Don't know what we did wrong.
 
PS. I almost forgot. Before the molly died I noticed something was wrong, we was swimming belly-up, he seemed to try and turn around but every-time he'd end up belly-up and floating towards the surface.

 

[FilipeB]

Another update, I just learnt that damselfly larvae has got 3 tails, whilst the one I found only has 2. Also it's color is a lot more bright green than any of the damselfly larva photos I see on the internet. Any idea if it is really is a damselfly?
 
I think I'll also post this on another forum section that makes more sense.
 
P.S. How many shrimps do you think I can have in my tank? I really like the yamato shrimp, so I'd like to get quite a few more