New Guppy Problems.

A few weeks ago I lost many of my female guppies following a sudden pH drop. This left me with 4 males and 2 females. I fixed the water problem but decided not to add more fish for a few weeks to allow the survivers time to recover. Yesterday I added 6 new females to restore the Ballance of males to females. This morning one of my males had half his tail missing and I saw both the other males and the new females attacking him. I moved him to a hospital tank but he soon died. I have never had a guppy attacking another guppy before. Now my remaining males that usually dart around the tank are hiding in the corners. I have checked the water and nothing is wrong with it. The new fish have been quarantined for 3 weeks. Has anyone any ideas?

 

I have had this happen to me before. Sometimes when more females are added to the tank, males will start to compete more with each other. Now I haven't had it so bad I lost some fish, but it seems like it was just some fighting over dominance.

 

I hope your right. I seem to have a blind spot when it comes to guppies. I have had guppies for years and I have never gone more than a few months without problems. I have many other tanks with other fish that I have kept successfully many I have had for years without deaths. I often think I should give up on guppies but I don't want to give up and let them beat me, I am determined to master them eventually. The tank I keep them in was my first ever aquarium but I wonder whether it's not very good. It's an aquael sphere with a built in filter that covers half the surface and a light above it so half the tank is dark. The only other thing in the tank is a dwarf suckermouth catfish who has been in for years. There are some live plants in the tank some on the bottom and some floating.
The test results are as follows
Ammonia 0
Nitrites 0
Nitrates 5-10
PH 7.5
KH 5
GH 4
Temp. 25.5 C
I change 25 percent of water twice a week
I have coral sand in the filter because my tap water is very soft
I have some fry in the tank but most my fry develop with curved spines so I just dispose of them.

 

how big is the tank

 

It's supposed to be 68L but once allowing for substrate it only holds 60L.

 

Yeah it seems fight for dominance. Even in my 75 gallon male guppies fight over females

 

Don't start panicking if you are. One of the best things you could do to your guppy tank is add a little bit of aquarium salt to it, it brings down the stress level a lot and also acts as a preventive method for fish dying early. If all the readings are normal then add some aquarium salt, its bound to stop the fish from dying