Very Sad Fish Massacre

curiousburke

Most of my adult fish died tonight. Ive always done big water changes every few weeks without a problem, but I did a large water change today that caused a massive fish die off. The dead are:
6 rosey barbs
2 SAE
3 cories
2 rainbows
5 giant danios
2 adult Kribensis

The survivors so far are:
3 cories
5 rainbows
30 young kribensis
100 new kribensis fry
1 large gourami
7 otos

So, the survivors were the smallest fish in the tank except the gourami. The 2 cories and 2 rainbows were the last to go. The only thing that was a bit odd was that the water was very aerated.

What do you think did it? Some thoughts:
1) big water chemistry change, but why this time and not before?
2) soap, would that be less lethal to small fish
3) temperature shock

Calmwaters

So sorry for your loss. It could be either of the things you mentioned. What did they do before they died? Such as swim side ways, or stay at the top of the tank for example. How would you get soap in your tank? You should always have a bucket that is only used for water changes. Do you have city water or well water?

curiousburke

they swam funny, some upside down or in circles. Some jumped out. Distressed for sure. In the end they all floated before they died. Actually, that's not true, some sank.

I fill with city water and treat in the tank with prime. I put the prime in before the water. I've been doing this for awhile though. I use a hose straight to my kitchen sink. The only way soap could get in is if my sink backed up while the dishwasher was running. I don't think this happened, but it is a possibility. In this case a little dish water could have got on the end of the hose. If it was soap would you expect that to spare the babies?

Calmwaters

Sounds to me like they went into shock either due to a major swing in temp. or ph but I am leaning more towards temp. It maybe that the adult fish swam through the incomeing water while the babies and smaller fish stayed out of the way. It is very important when changeing water to keep the temp close to the same temp as whats in the tank.

curiousburke

between pH and Temp, I would guess temp. I did correct the temp upward a couple degrees after they started swimming funny, but they just kept on dying.

Calmwaters

Temp shock kills them pretty quickly.

curiousburke

how many degrees would I have to be off? How could this explain that my largest fish and all my small fish survived.

Calmwaters

Maybe the affected fish were closer to were the water was going in the tank not sure just a guess. The temp would not have to be off by much to put the fish in shock. It may not have been the temp but the way you described what they did makes me think it was the temp. Someone else may come along and have another idea or know why it affected some fish and not the others.

Byron

This is difficult to pin down without some data. Leaving aside any toxic substance like soap getting in the water, the most likely explanatio is a considerable fluctuation in the water parameters: hardness, pH, temperature, ammonia/nitrite/nitrate, metals, chlorine... . Any one of these could be the issue.

Do you have any idea of the pH, nitrate and temp prior to the water change, and then after? A tank's biology can change considerably in two weeks, and especially if the fish load is higher rather than lower, feeding amounts, plants, etc. This might well lower pH and/or raise nitrates to the extent that the new water would be vastly different. This is one reason why water changes should be more frequent, weekly at minimum; it creates more stability.

As not all fish were affected according to what you describe, we can probably rule out chlorine as this would have poisoned all the fish quickly or equally. A significant change in pH or nitrates would affect different fish differently. Temp too.

Byron.

curiousburke

Well, I know the pH before was about 7 and after was a little higher about 7.2 or 7.4. I find the scale difficult to read in that range. Its certainly a smaller pH change theh I has done in the past, so Im pretty sure it is not pH.

I dont know the hardness. I do know that I add baking soda periodically to keep the pH up, so if that raises the hardness then there would have been a drop in hardness with the water change. I have been doing that more recently so the effect this time might have been bigger. I've never lost fish with a water change before.

I did not check the nitrates before, but knew they would be high, which is why I did a big water change. I am overstocked and it was a little longer than I usually go between water changes. They are between 20 and 40 now, so probably 100 to 150 before.

I have not lost more fish since last night, which is a relief. However, I don't know if I can save the kribensis fry. They are out of the cave now, which they never have been before, and just waiting around. I put another small tank upside-down over the area to protect them from the rainbows, but some have somehow escaped. I did feed them some baby brine shrimp, but I'm not sure if they can even eat them now. All the other batches had a very good mom to protect them through the early days.

hardness or water temperature makes the most sense to me. The water temperature before was 74 (that is the temp now, so it should have been the temp before since I have not changed the thermometer) and the temperature after was 72 maybe as low as 71. The swing couldn't have been more than 4 degrees.

Are gouramis really, really hardy fish? Whatever did it mostly killed large fish, except my gourami which was by far the largest fish in the tank.