Danio Behavior - tail sinking, lethargic

I have 5 danios in a ten gallon tank with two ADFs. Lately the fish have been just hanging at the top of the tank with their tail ends sinking a bit. They will wiggle back up then start to sink again. None of them are bloated, gasping or otherwise illl-looking. Sometimes they will dart around and chase each other but mostly they just hang there. I have four live plants in the tank and my filter seems to put quite a bit of air into the tank as well. I tried feeding them some blanched pea - reading that it could be a sign of disease, but none of them would eat it. I have fasted them for 24 hr but they were eating normally before.

Stats:
Ammonia - 0.25. Doing 20% water change daily. Tank is still going through initial cycling. Been established for three weeks (two without fish and one with)
Nitrites - 0
Nitrates - 0
Ph - 7.5
Gh - 150
Temp - 75

Frogs are acting normal (thanks to everyone who helped me with that on my other post!)
I keep the tank as clean as possible. Using a vacuum for water changes and even feeding frogs in a temporary enclosure. Plants seem healthy - no dead leaves.

Any idea what this could be and how to help them feel better? Could it be the gh? Our water is very hard. Yes I am using a conditioner and taking readings with the API master test kit.

 

I am now down to three danios. Water parameters are good. Tried to feed a pea again. Any advice anyone?

 

What type of danios? Is the ammonia still at 0.25?

 

I'm now down to two. One long fin zebra and one gold. Ammonia still the same - actually a little lower. The one who passed appeared to die from constipation related issues. Still can't get the others to eat a pea. Even if I put them in a small tank with nothing in it. I even tried holding it right in front of them...

 

Sorry for your losses.
Ok, so I have a few ideas of what might be wrong with them. First, the ammonia. They may still be suffering from ill effects, even though it's been going down. Second, the tank is too small for them. These are very active fish when healthy, and they may be feeling stressed from the limited space.