Came home to a really sick fish

[Maura]

I was gone from work for 5 days and during that time, a coworker (who doesn't usually deal with the fish) decided to change the water in the betta tanks. She changed the water on Saturday and I came back on Monday. Turns out she used RO water with Prime, instead of either tap water with Prime or RO water with RO right and Neutral Regulator. Oops.

Anyways, one of the bettas is in really bad shape. I think I caught water mix-up problem in time for all the other bettas in the tanks, but this one is really badly off.

Housing
What size is your tank? 20 gallons
What temperature is your tank? 83º
Does your tank have a filter? Yes
Does your tank have an air stone or other type of aeration? No
Is your tank heated? Yes
What tank mates does your betta fish live with? 6 bettas in a divided tank (~3.3 gallons/fish; please keep in mind that this is a pet store!!!)

Food
What type of food do you feed your betta fish? Hikari Bio Gold
How often do you feed your betta fish? 1x daily (3 pellets, again keep in mind that this is a pet store!)

Maintenance
How often do you perform a water change? every Monday or Tuesday, since our fish shipment comes in early Tuesday afternoon
What percentage of the water do you change when you perform a water change? 50%
What type of additives do you add to the water when you perform a water change? RO Right or Equilibrium for RO water, Stress Coat for tap water (water used depends on tap water pH, as it is unreliable in my town)

Water Parameters:
Have you tested your water? If so, what are the following parameters?

Ammonia: 0ppm
Nitrite: 0ppm
Nitrate: <20ppm
pH: 7.0
Hardness: I forget, can test in the morning if needed
Alkalinity: I forget, can test in the morning if needed

Symptoms and Treatment
How has your betta fish's appearance changed? Slime coat sloughing off, fin melt, rapid gill movement
How has your betta fish's behavior changed? Lethargic, no appetite
When did you start noticing the symptoms?
Have you started treating your fish? If so, how? 90% water change Monday morning (yesterday) using tap water treated with Stress Coat. Added additional Stress Coat this morning.
Does your fish have any history of being ill? No.
How old is your fish (approximately)?~4 months

What, if anything, can I do to help this betta? I've never seen a fish this bad other than the one who jumped out of the net into the sink (and there the slime coat issue made sense).

[Maura]

Bump

[Maura]

Bump. Again. Come on, please?

[JeannaAnne]

I don't know much about this because I don't usually add anything other than salt into my aquarium water, but from what you've said, it sounds like the electrolytes in the fish may have been leeched out by the RO water and he may have ended up absorbing too much pure water which could have caused cell damage since RO water is hypertonic. The damage is most probably internal, and in his gills and fins, since they would have come into direct contact with the pure water when he breathed and swallowed the water. (And betta fins are really thin and delicate)

Right now I can't think of anything to reverse that, cell repair will take time and he was exposed to the water for a day, but since the cells in his gills are likely damaged/have burst, he probably can't get enough oxygen. Is there any way you can get more oxygen into the water? It's probably a good thing that bettas also have a labyrinth organ, but since it would also have come into direct contact with the water, it probably got damaged too. In the meantime, you can lower the water level so it's easier for him to surface for air.

I'm not sure if you should place more electrolytes and nutrients in his water now because it might just dehydrate him, but right now I think the biggest problem is that he can't breathe properly.

I'm sorry about the poor fish :\ I hope this helped some.

[Maura]

Too late. He was dead when I came into work this morning.

[LebronTheBetta]

RO water is tap water without the minerals, correct? If so, he's in shock because there's water in the tank that is basically useless to him.

I suggest for you to put him in a QT tank, and add Aquarium Salt. 1 teaspoon per gallon. The water should be tap water and your conditioner. The Aquarium Salt will probably help with his stress coat. Add in some IAL or Oak Leaves to put in some soothing properties. What you want to do is cover the tank with a blanket so he feels safe and even more comfortable in darkness. Keep the temperature the same. And make sure the water changes are not that stressful. I hope he gets better and no more RO water! >.< EDIT: I'm so sorry!! I guess I was too late...

[Aus]

Just wanted to say -- thank you -- for a most informative reply - I learned a lot from it!

Originally Posted by JeannaAnne

I don't know much about this because I don't usually add anything other than salt into my aquarium water, but from what you've said, it sounds like the electrolytes in the fish may have been leeched out by the RO water and he may have ended up absorbing too much pure water which could have caused cell damage since RO water is hypertonic. The damage is most probably internal, and in his gills and fins, since they would have come into direct contact with the pure water when he breathed and swallowed the water. (And betta fins are really thin and delicate)

Right now I can't think of anything to reverse that, cell repair will take time and he was exposed to the water for a day, but since the cells in his gills are likely damaged/have burst, he probably can't get enough oxygen. Is there any way you can get more oxygen into the water? It's probably a good thing that bettas also have a labyrinth organ, but since it would also have come into direct contact with the water, it probably got damaged too. In the meantime, you can lower the water level so it's easier for him to surface for air.

I'm not sure if you should place more electrolytes and nutrients in his water now because it might just dehydrate him, but right now I think the biggest problem is that he can't breathe properly.

I'm sorry about the poor fish :\ I hope this helped some.