Large Die-Off after water change

[Colin_T]

Was that the only tank water changed on that day?

It definitely sounds like poisoning caused by the water change.
The two options are contamination by something that got into the tank, or toxic tap water.

 

[Lajos_Detari]

Usually when you have few fish died at the same time, there must be a strong chemical/ toxic in the tank.

I can only think of :
1)Any insect repellent, cleaning detergent or chemical being sprayed near the tank
2)High chlorine in the tap water, etc.

In my country when there are continuous heavy rain for a few days, the Water Dept officer may tend to put extra high chlorine in the tap water.
Sometimes you can even smell the Chlorine in the water.

In my opinion, most fish can withstand slight ammonia in the water for some time. If you observe the fish stores, some have super overcrowded tanks and yet the fish can survive until they are sold off.

Just some extra info:
Your temperature change at 84F is still ok.
During a hot afternoon, if I change 90% of my tank water, the water temperature will swing from 86F to 90F.
I never have any fish loss due to my water change and I also have a Killifish in the tank.
But nowadays I try to change water in the late afternoon or evening time so that the water won't be too warm.

 

[Jan Cavalieri]

Back again - I've had two more incidents since this one occurred. One I lost 12 fish then today I lost 2 - several others were semi-unconscious but came around. I think the water was too warm but thermometer had it at 80. I think it's the PH. We always add acid reducer to each bucket of water to try to ensure that the PH is close to the same as the tank's. Our city water (same as mine) averages a PH of 9.4. By adding the Acid Reducer we will get the water PH in the buckets to about 7 - by then the PH in the buckets is USUALLY dropped to 5.6-6.4 over the course of the week. Adding the Acid reducer brings it up to about 6.4 - ie., it's fairly gentle. If it's a lot lower or higher then I add PH down or PH up which is much more risky. Well today (as in the other two times) I didn't check the PH in the tank or I would likely have noticed it was in the 7's instead of the 6's. So when we poured the solution it went up to a little over 8 an fish immediately started dropping and I got my PH down and poured a capful in - too much I fear because the PH dropped a LOT. Several fish looked dazed but none died. Lost my last neon tetra (previous 5 died the last incident). I have yet to replace the fist from the first incident until they have some in that I want. OH - and this has ONLY happened in one certain tank - nothing unique about it - just one of my regular glass ones but it's never happened in the other glass tank (which has really big fish) and the other two tanks are acrylic. I just made the mistake of not testing as well as lowering the PH too much too fast.

My conclusion is to always measure the PH in the tank BEFORE we start mixing water and use more or less of the acid reducer depending on the reading in the tank. I am so sick of killing these poor fish because of my sloppiness and my city's bad water - if it was normal I wouldn't touch the PH.

Any other suggesstions (or beatings) for me.

 

[StevenF]

Perhaps too much Prime was used in the new water. Overdosing prime during a water change has cause fish die off for other people.

 

[Colin_T]

If you are going to adjust the pH of new water, do it in buckets or holding tanks 24 hours before using that water in the main tank. Aerate the buckets of water and check the pH 24 hours after adding the pH adjuster. If the pH is where you want it, then use the water for water changes.

pH adjusters can continue to change the pH for hours after they were added.

 

[Jan Cavalieri]

Colin - sounds like a good idea. Love the sight of buckets of water all over the house - but I do have enough buckets to do it. Right now I made an interesting discovery - my PH meter is way off - it's showing pH's of 12 but when I do test tube testing it's just below 8 which means I should have no need to use PH+ or PH- and lord knows what the REAL ph was when all those fish died off - a PH of 8 shouldn't kill any of my fish. Not going to use the meter again until I can get more calibration chemicals and see what's going on. I trust the test tube method more any way. I HATE our city's water - I have no desire to add chemicals - it always feels too risky.

 

[Jan Cavalieri]

Oh and to answer your first question - no - one other tank's water was changed the same day. The 3 instances I have had are always the SAME tank. No incidents like this with the other tanks. I do think one of the incidents that killed most of my small fish was when my assistant just dumped 5 gallons of water in the tank - fish went crashing into walls - some were unconscious but came around, most just died. She knows now to slow down on the water pouring and give the fish a chance to get away. Of course the Dojos just loved iit - being long and skinny they just rolled around and handled it quite well. They love drama.

 

[Byron]

You are using pH adjusting chemicals and this is without question harming the fish, weakening them every time you use it. And the fact that the pH is fluctuating is another problem, due to the adjusters. It will have a detrimental effect. Fish crashing into the tank walls is not going to occur from water flow, but from differing parameters that shocks them.