[Diver Down]

I lost a 6 month old Zebra Danio today following a routine 25% weekly water change. He shared a 20-gal tank with two other Danios and six tetras (Rosie and Red Phantom). The whole gang seemed fine before the water change, but all were acting panicked right after. My first thought was to look at the water temp, which it turns out had risen about six degrees. I keep the tank at 76, and my thermometer was showing 82. A few minutes later the Danio was dead, and one of the tetras was lodged at the base of an Anacharis, breathing but not moving. Now the tetra is swimming again, but he is still weak.

I also tested Ammonia, Nitrites, and Nitrates after discovering the problem. Zero ammonia, zero nitrite, 20ppm Nitrate. That's typical for my tank. Also tested pH. Read 7.2, which is a bit below typical, which is 7.4.

So, could a six degree rise cause such a sudden trauma? Nearly instant death? Clearly, the water I added must have been considerably warmer than 82, if it caused the blended temperature to rise to that level. But the water I added felt cool to the touch, with a slight stream of warmer water mixing in. Certainly not hot. I fill the tank from my tap (separate hot and cold valves mixing in one faucet), testing and adjusting the temperature beforehand. It's not an exact method, and sometimes the pressure on one of the two taps will drop after I start filling, changing the blended temp. That may have happened this time; the only evidence I have is the temp rise.

-DD

 

[scott1234]

In my opinion, Yes, a sudden 6 degree temperature fluctuation (in either direction) will kill fish FAST. My method, that has worked perfectly for years, Aging my water. What I do for all my tanks is, for my 20 gallon I do 50% weekly W/C, which is 2 5 gal. buckets, filled and let sit in my bathtub 48 hours prior to W/C. The reason for this is the water straight from my tap has a PH of around 8.4, after it has a chance to sit, it settles to 8.0. Plus the chlorine has a chance to gas-out naturally (I still use seachem prime just as a precaution) so after all that your water is completely stable, I never use straight from tap, it only causes problems with fluctuations in my tanks. NOW temperature wise, Get yourself a meat thermometer ( I know how it sounds but bare w/me) they are shockingly accurate (I crossed tested against aquarium thermometers) test water temp. in buckets, for me, my aged water always reads 68-70F, so I plug the tub and fill with hot water about 1/3 up the side of the buckets, give the buckets a stir every 10 minutes or so, keep checking the temp. of the bucket water, in 20-30 minutes, my buckets temp. match my tank temp.

 

[henningc]

I concur the change in temp did the damage. Aging water is a great way to make sure things are stable. I have a heated fishroom, so my 5gal buckets are always the same temp as the tanks.

 

[pop]

Hello:
I am not challenging you all assessment but this loss of fish due to temp change 6 degrees is hard to understand. One might think that since only one critter passed on why didn’t the other aquarium members also pass on if loss was due to sudden slight temp change of six degrees.


I think you had to add very warm water to you 20 gal tank to raise the temp that much. I would check the heater. When I do water changes I use cold water unless I am doing a 50 % or greater water change.


the sudden change in pH could be connected to the problem by way of tds shock. there are some good articles about total dissolved solids and total suspended solids in the article section.

pop

 

[Diver Down]

Thanks for the tip, pop. I located the article on TDS. Interesting indeed. I too was skeptical that the temperature rise - even if it really was six degrees - could have such an immediate impact. That's what motivated me to post here to see whether others have had any similar experiences.

The article indicates that if Total Dissolved Solids are high in a tank, fish may struggle more to adapt to any change in pH. The use of the term 'TDS shock' (as the root cause behind pH shock) suggests to me that the impact can happen very quickly. But I'm still not clear how much of a change is considered significant.

Is a shift from pH 7.4 to 7.2 a big one?

Similarly, I'm not sure how suddenly the pH dropped. I had not tested it for a few weeks, and I did not test it immediately prior to the water change.

I monitored pH regularly both in the tank and at the tap when the tank was new... January through April of this year. My API kit consistently indicated a pH of 7.4 for both sources. During the spring, I reduced the frequency of my testing. I do partial water changes every week. Last night, the lower pH was evident both in the tank and in the tap water.

So it does appear that something changed in the water supply. Perhaps the city made a change in the treatment process at the start of summer. I don't have the ability to test GH, and I imagine GH/KH could have changed as well. Probably time to purchase one a test kit. Any suggestions?

-DD

 

[pop]

Hello Diver Down:


I cannot offer much help or any valuable suggestion due to my lack of knowledge and experience. My understanding of pH is that pH 7.2 is two times more acidified than a pH of 7.4. Another way to view the difference is that pH 7.4 has twice the amount of hydroxyl ions as hydrogen ions making the solution alkaline. When pH change is integers (whole numbers) the difference is tenfold, so a pH of 8 is 10 times more alkaline than pH of 7.0 and a pH of 9 is 100 times more alkaline than pH 7.0


To answer your question small changes in pH can represent large differences in the concentration of the hydrogen / hydroxyl ionic relationship.


How pH impacts water critters I don’t understand.


pop
(In Bryon's article on tds the effects of CO2 on pH is not considered)