Heavy rains changing tap water pH?

[V_man]

We have had about 4" of rain over the past week here in northern IL. I went to do a 50% water change/gravel vacuum today and these are my pre- and post- pH levels.

Pre water change pH ~8.2

Post water change pH ~7.4

After seeing this, I tested the water directly from the tap and it was ~7.4. The water out of the tap has been hard and in the 8.0 - 8.2 range for as long as I've had the tank, and the tank pH wouldn't ever vary from before to after water changes, until now. The only thing I can possibly attribute it to is the recent heavy rain diluting the water supply. I (obviously) didn't expect this to occur and I am a bit worried about my fish enduring such a drastic pH change in only a few minutes. They all seem to be acting normally so far, still very active and social as usual. I have 5 gold barbs and 3 zebra danios. Also I fully expect the tap pH to come back up at some point, I will just test it before do any more water changes. But fluctuating pH can't be good for my little dudes and dudettes.

Anyone else ever experience this?

Vince

[Fresh2o]

It should be fine. You could try reducing the WC amount to 30% and performing it 2x a week until the pH returns to what you are used to seeing.
Interestingly, this kind of change sometimes induces spawning in certain fish such as tetras.
You could try putting some tap water in a glass and letting is sit overnight to see if the pH is the same. Ditto with the tank; take another reading tomorrow.
I don't check my pH anymore. When I did, I would see 0.5-1.0 swings on a daily basis; it's a planted tank and CO2 injection can influence pH readings.

[McClapyourhands]

Hey! I read this post earlier today, then completed a water change. While I had the same problem! My PH levels spiked. I live near upper IL where the rain hit as well.

[Autumnsky]

Agree with more frequent and less amount pwc. = less drastic changes for the fish.

[V_man]

Originally Posted by Fresh2o

It should be fine. You could try reducing the WC amount to 30% and performing it 2x a week until the pH returns to what you are used to seeing.
Interestingly, this kind of change sometimes induces spawning in certain fish such as tetras.
You could try putting some tap water in a glass and letting is sit overnight to see if the pH is the same. Ditto with the tank; take another reading tomorrow.
I don't check my pH anymore. When I did, I would see 0.5-1.0 swings on a daily basis; it's a planted tank and CO2 injection can influence pH readings.

Thanks for your input. Haven't had a chance to get back on and update but I did what you suggested that night and you were right, the pH came back up both in the tank and in a glass of tap water over night. Tap pH is getting closer to normal. The fish weren't visibly affected and after reading what you said about your pH changes I am not too worried about it. I usually do a 20% WC 2x week and then every other weekend a full gravel vacuum with however much water it takes out in the time it takes to vacuum the whole tank which is usually about 30%.