Sick Rainbowfish

One of my female Boesemani Rainbowfish is sick and I can't figure out what's wrong with her. She is hiding in the corner with the most current, just undulating back and forth. She is not interacting with the other rainbows or eating. Her colour is very pale and blotchy. She has lost all the orange at her tail end. (I have attached a photo.)
 
I recently moved all of my fish into a new tank, so this might have something to do with it, but I'm not sure because all of the other rainbow fish are fine. When I changed tanks I cleaned out the new one and filled it almost half full with treated tap water and let it sit for 24 hours. Then I moved the filter, heater, decorations, and gravel from the old tank to the new tank. The fish waited in a covered bucket for about 45 mintutes (I could hear them clunking around in there - so I worry she may have hurt herself.) Then I started up the new tank and added the fish from their bucket of old tank water. The new tank is almost twice the size of their old one and contains all their old water, gravel, filter, etc, (so no cycling required) and has an additional (well washed) package of gravel and about 40% treated tap water. So from my point of view, this should be essentially nothing but a 50% water change into a larger space. All the other fish seem to be adjusting well and enjoying the space the 50 gallon is allowing them.
 
Initially the nitrites went up a little bit in the new tank, as did the nitrates from disturbing the gravel. I did two 50% water changes, one today and one yesterday. And I added a couple of plants. I added a bit more aquarium salt and raised the temperature one degree.
 
Yesterday morning the readings were as follows:
Temp: 75
Nitrite: 0.1
Nitrate: 15
Ammonia: 0
pH: 7.0
KH: 80
GH: 120
 
Today the are:
Temp: 76
Nitrite: 0
Nitrate: 5
Ammonia: 0
pH: 7.0
KH:80
GH:120
 
Everything in the tank seems fine to me, but I must be missing something! Does anyone have any more ideas of what I could do for her? She's only three years old.

How big is the new tank (dimensions please, not volume)? Bosemani (like the other >8cm as adult species) rainbowfish need a good sized 4-footer as a minmum, they are active fish.
What other tankmates are there (species and quantity)?
How much water do you normally change per week? 50% is seen as a standard minimum for rainbowfish, "cotton mouth" amongst other diseases tends to show its ugly head otherwise.
Why is you nitrate level so low? Liquid nitrate kits need banging and shaking for at least a minute for a vaguely accurate reading, reagents settle on the reagent bottle floor.
 
Another thing I picked up on from your post is your low hardness readings, 80mg/l kH and 120 mg/l gH sounds awfully low for hardwater fish like rainbowfish and could be the root cause here (with this specimen more sensitive than the others), tap water like I have with ~200-240mg/l for kH and gH is far more suitable.
 
http/www.seriouslyfish.com/species/melanotaenia-boesemani/

so sorry, your fish already dead!

hey can you stop posted on every thread saying the same exact thing? your offering advice and we can still help save their fiish, the only thing your doing is creating a disturbance.

@ncguppy: don't be mad my friend, the truth is ugly, you know that...his fish dead or not, you just ask him...then you see what i told you is right, as i can see, his ranbow lost too much slime, cause of a fish in his tank do that or the water have problem, i can't guest exactly what happen, but in this situation, we can't help him.

Stop trolling everyone's threads huc...PITA

ncguppy830 said:

hey can you stop posted on every thread saying the same exact thing? your offering advice and we can still help save their fiish, the only thing your doing is creating a disturbance.

Click to expand...

 
+ 1

My fish is still alive and is now eating, but she doesn't look much better. The tank is 4' long by 19" high by 13" deep. The tank contains 8 neon tetras, 6 rainbow fish - 2 turquoise and 4 boesemani (hoping to get a couple more turquoise, but obviously not while one is sick), one kuhli loach (again a few more on the way after rainbow fish is better), one clown loach, one wood catfish, one bristlenose pleco, an amano shrimp, and a lone (elderly) cherry barb.
 
Our tap water contains almost no nitrates, so I assume the numbers are very low after two days in a row of doing 50% water changes to get rid of the nitrites that appeared after I disturbed their old gravel and moved it into the new tank. Normally I do 50% once a week. The hardness was higher in the old tank. I don't know why it dropped... could that be the problem? How do I get it back up?
 
I was wondering if it was something fungal... should I try to treat for that? She doesn't seem to have any patches growing on her or anything, but she's lost her colour in random places, mostly near her belly. One of the neons seems to have the same thing and developed it at the same time, but none of the other fish are showing any signs.
 
When I test the nitrate I shake it well, wait 4 minutes, and then shake it for a minute before reading it. It is still very low today too. And the pH has gone up to 7.1 today.
 
She's not getting better, but not getting worse... I think there's still hope...

Ok, I think I figured out what her problem might be. The dominant male has been chasing her a lot (she's the largest female) so I called all around, finally found someone with large, female, healthy Boesemanis and bought two of them. I feel a bit bad for them because he was chasing after them this morning, but he was totally leaving the other female alone and she was much perkier and even had a bit of colour back. With three females, equally as large, it should take the brunt off of her. Sorry huc1115, you were wrong.