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Temperature Shock?

12726 Views 5 Replies 4 Participants Last post by  pop
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.

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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?

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