Three dead... And counting?

[sophiamarvv]

Over the past two weeks I have lost three guppies. Two of the three that died had no signs of anything wrong. I don't know what what is going on.
Changes in the last two months: started using plant food. I do 5ml every other day. I added a paradise gourami a week ago along with one of the guppies that has since died. And I got packaged dwarf hair grass. Could it be my plant food killing my guppies? This one died today, I guess in the middle of my water change. And to avoid a water change question, I add prime BEFORE I put it in the tank to avoid any chance they get exposed to unhealthy water. I hadn't lost a fish in this tank in almost 5 months and now one I posted a different thread about has I guess dropsy.
But the three that have already died have no symptoms. The one today wasn't even acting like anything was wrong. Could it be my plant food?
Water parameters as of just four days ago: 7.0 ph, amm .25, 0nirite, 20 nitrate.
Now these parameters are different than what most of these fish are used. Before adding the gourami and the other guppy my water was steady 7.2,0,0,10. Could this be causing a problem? Maybe I am having a mini cycle?
Please help I don't want to lose anymore fish.

 

[sophiamarvv]

This is the latest dead one. It has a red dot on the side that I thought may help. Could it be an internal parasite attacking fish?

 

[emilygupps]

You know what, I have a sick danio and we just fed the plants Tuesday. I wonder of that's related. Thanks for the idea I hadn't considered that.

 

[sophiamarvv]

Water wise it's the only thing I've changed so my idea was that maybe I'm feeding them too much and the nutrients are too much in the water.