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Harlequin rasboras dying one by one

5336 Views 2 Replies 2 Participants Last post by  paperlilies
I just bought 4 harlequin rasboras 3 days ago. I was planning to buy 6, but the fish store only had 4 left. I acclimated them to the new water for 1 hour. Pouring 1/4 cup aquarium water in their plastic bag every 5-15 minutes. They seemed great for 24 hours. Then one by one died 24 hrs apart overnight. I'm left with 2 now. I expect to have only 1 tomorrow morning. The strongest rasbora is picking on the weak one.

Only signs of sickness:
-leaving the shoal group to hang out by it's self in a corner
-mouth and fins twitching/pulsing closer to it's death
-not eating closer to it's death
-loosing color

Suspected possibilities:
-they were in the car driving home for 45 minutes - temperature fluctuations
-bought a bad batch
-acclimating in 1 hr was too fast. they went from neutral ph to 8.0
-TDS is 300ppm

It's a 10 gallon low tech established for 1 year
heated to 76 degrees
2 HOB aquaclear filters and 1 sponge filter
inhabits: 25 red cherry shrimp (healthy and breeding) and 1 male betta (He doesn't bother anyone. I keep him well fed.)

Ammonia: 0 ppm
Nitrite: 0 ppm
Nitrate: 0-5 ppm
GH 6 degrees
KH 4 degrees
pH: 8.0

No Co2
Ferts: seachem flourish 1/2x/week, root tabs (3 months)
plants: java fern, duckweed, crypts, christmas moss


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I had the same issue in my planted tank, my problem was the water in my office had to high of a PH, Harlequin Rasboras do best in a PH with 6.5 to 7 PH, I am think that is your issue. I added Poland Spring water to my tank when I did a water change and it brought it down, this might help you.

Bump: When my PH was too high the fish would not eat and breath very heavily, they would swim in circles before they died, if this is what is happening for you then I highly recommend lowering the PH.
When I set up my tank a year ago, I tried to soften the water by mixing 25% RO and 75% TAP. The tank had dangerous swings in pH, GH, and KH for 4 months. I didn't add fish until it was stabilized by using 100% TAP water. Knowing stable pH, GH, and KH are better than fluctuations, I gave up. My substrate is designed to buffer the water and bring the pH to 6.5-7.0. I think that is where the swings were coming from.
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