Erratic Ph levels

[big1521truck]

I maintain a 200 gallon freshwater aquarium and am running into an odd situation. It is a well established tank (over 5 years). I did a cleaning and 25% water change this past Friday. I did it the same way I always have and have never had any issues. Saturday evening I checked water quality levels everything was perfect except Ph. it was at 6.0 so I added some Ph up to raise it. Checked it on Sunday it was at 7.8 (where I like it keep it) On Monday checked again it was back to 6.4. Left the tank alone to let everything balance out and see what it was going to do. Today checked it and it is at 7.4 I have had aquariums for 10 years and have never ran into anything like this and really not sure what to do. The fish are acting normal so should I be concerned with Ph fluctuations this drastic?

Also I checked with multiple Ph testers. The aquarium is located at a veterinarian office so I used their machine for checking Ph in urine to verify my tester is accurate.

Thanks in advance for any advice
Thomas

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[Mebbid]

How often do you do your water changes?
Are they always 25%?
What do your nitrates hang out at?
Have you tested dKH?

 

[big1521truck]

With this tank I do water changes about once a month. 3-4 weeks
Yes normally around 25%
Nitrates are normally around 0-5 ppm in this tank I have never seen them high.
No I haven't tested dKH I'll try to get over there tomorrow and test that

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[Mebbid]

Tanks will have a pH crash as time goes on if the water isn't changed enough. The BB that consumes the ammonia and nitrite also consume the dKH which buffers the pH.

The dKH can be supplemented, but by far the safest way to supplement it is by increasing the water change schedule.

 

[big1521truck]

Ok that makes sense. I will talk to them and see if I can start to change it more often. With my personal tanks I do water changes every 1-1.5 weeks. The only reason I do it once a month is they said the company that did it in the past only did it one a month. I took over doing it 3 years ago only because my wife works for the vet and I started to "help" them out. Which I don't mind I enjoy messing with them. A tank that size how often should I change water? Also with the more frequent changes should I still do 25%?

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[Mebbid]

If the nitrate levels that low I would suggest twice a month since it's likely lightly stocked. I'd bump it up to 50% if possible.

 

[BBradbury]

Your 200 G

Hello big...

Interesting you haven't lost fish since the pH scale is logarithmic and even very small changes can be lethal to aquarium fish. The small water changes won't do much to steady the chemistry and attempts to change the pH aren't recommended. As long as there are no exotic species in there, there's no reason to fret over the chemical makeup of the tap water. The fish available at the local pet stores will adapt to most public water supplies, so there's no point in testing the hardness, pH or any of this chemistry stuff.

If I was maintaining the tank, I'd work up to changing out half the water weekly, a large task in itself considering the size of the tank. This alone will keep wastes from accumulating in the tank water and maintain a level water chemistry. This the most important thing for a healthy tank.

B