Random deaths of Tetra's!

[Puddle]

I bought 7 young cardinals 2 wks ago and added them to my 6 month old tank, all were happy and eating and active, until day before yesterday one of my old cardinals died (put it down to old age as was about 5yrs old) but last night two of the young new one's died too , they all looked healthy yesterday morning so I don't understand whats going on :?

Have a 40 gallon tank with 1 SAE, 2 dwarf gourami's (still healthy at the mo, wouldn't like those to go :? ), 4 harlequins, 2 guppy's and now only 7 cardinals so not overcrowded. Nitrite 0, Nitrate 25ppm ish (colours difficult to read, may be higher) and Phosphate 0.5ppm

The only thing I did differently was perform a blackout last week (I had BGA) did a water change and added some liquid ferts (10ml Plant nutrition +) as my plants weren't doing well. I usually do weekly PWC.

After finding the dead fish, I did a quick small water change in case the nitrates were a bit high. Fingers x!

Any ideas/help really appreciated!

 

[black hills tj]

Sorry if this post seems useless, but it seems like there have been a lot of mysterious deaths recently in several people's tanks. Often they have shown no signs of illness at all and perfect water levels

 

[Puddle]

So any ideas?

 

[rich311k]

Could you post a full set of water tests? Are the remaining fish looking ok?

 

[Puddle]

Hi

pH 7.6
Nitrate 5mg/L
PO4 0.5mg/L
Nitrite 0
All other tests in normal ranges

All other fish are looking very healthy, though I lost another old cardinal over the w/e

 

[vfc]

Do you add de-chlor to your water? If so, do you add it directly to the tank during water changes?

I have a problem with my public tap water. I would loose fish within a day or two of every water change. Lost my neons, guppies, and blue rams. I now pre-mix my de-chlor (Prime) in a 35G trash can, circulate the water for a minimum of 1hr, then pump it back into the tank. Haven't lost a fish since.

 

[Puddle]

Hi yes I do add de-chlor and usually add it to the water before I put it in the tank, and give it a good mix around. Luckily had no deaths for 2 whole days, fingers x it continues!