# Water quality testing, before or after a water change?



## MSDdivers (Nov 24, 2014)

I know we do a water quality test whenever we suspect a problem but when it's part of regular maintenance do you do the testing before or after a water change? I like to do everything at once if possible.


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## DJRansome (Oct 29, 2005)

After the tank is established for a year...you may not need routine testing. I'd test after the water change to make sure your nitrates ended up where you want them.


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## plug (Nov 10, 2013)

I usually test before my water changes to see where the nitrates are and then I determine if I am feeding too much or if something else is wrong, like a dead fish or filters that are too dirty


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## BDASTRK (Dec 12, 2014)

Only time I do it now is if I see a dead fish, accept the last dead fish which was causd by my otter point decide he didn't like the Lethrinops anymore and beat him to death, that Lethrinops was 2 x his size. Watching him like a hawk now, if he does it again he will get the porcelain burial!!!


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## The Cichlid Guy (Oct 18, 2014)

Testing before you change he water will give you a more meaningful reading. If you test after, the levels will likely be lower than what they typically are in your tank. Testing before also lets you know what adjustments you may need to make when adding new water.


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## PhinFan1981 (Nov 15, 2014)

I usually test my water prior to a water change. I like this method because if anything needs adjustment I like to do it during the water change.If your tap and tank are close in P.H. then I agree routine checks may be unnecessary. My tap water and tank water differ too much for my liking. Another variable would be driftwood in your tank. I have it in one tank and if you don't keep up with regular water changes it can slowly lower your p.h.


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## BillD (May 17, 2005)

Testing before and after will tell you what effect the water changes has had. Doing only one or the other doesn't really give you much meaningful info.


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## PhinFan1981 (Nov 15, 2014)

Doing a test right after a water change is not meaningful info at all. If you want to test your TANK water then before and perhaps 24 hrs. after your change. If your adding 30-40% tap water to your tank (do the math) What are you testing??? I can assure you that testing right after a water change is gonna give you the most inaccurate result of what your tank is really doing.


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## BDASTRK (Dec 12, 2014)

PhinFan1981 said:


> Doing a test right after a water change is not meaningful info at all. If you want to test your TANK water then before and perhaps 24 hrs. after your change. If your adding 30-40% tap water to your tank (do the math) What are you testing??? I can assure you that testing right after a water change is gonna give you the most inaccurate result of what your tank is really doing.


This isn't entirely true either, Some people as described in another thread have **** water or high Nitrate water such as myself, before my Aquaripure filter I would schedule a water change as the Nitrates got above 60, only to put in water with sometimes 20 to 40 ppm. The test following would give me an indication as to where I stood with this test after. Not that this is significant to most but neither was your statement. Every situation or scenario does not work of the norm, and this case isn't any different, this is why the fact of every situation should come into play before making a general statement.

Also not that after 24 hrs my nitrates would not be much if any different then they where right after I took my test.


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## PhinFan1981 (Nov 15, 2014)

I guess if your tap water is as high as 40ppm for nitrate...that could be a rare situation. I didn't even think it was possible to have nitrate like that in tap water. That would drive me nuts.But even in this scenario if you test your tankwater at 60ppm then do a 40% water change with 20ppm tap water then common sense and a quick math equation will figure this one out. I stand by my statement even in this scenario. If my tap water was ****,I would test my tank prior to waterchange and test my tap water prior and that's a wrap.
In this same thread (BS-strk) said he never checks his water unless a fish is dead.Now he does after a waterchange? 25 years experience would teach me that a test right after a water change is unnecessary.


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## BillD (May 17, 2005)

If you know exactly how much water you removed a test after a change might be unnecessary. However, if you take the water down to a line on the tank or whatever you use to determine the amount to be changed, a test after the change would be helpful (allowing time for the new water to mix with the old.)


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## hisplaceresort1 (Mar 10, 2014)

I do both and log the info into a program called Aquarimate on my phone.

Most won't test frequently, if at all on a well-established tank, but I always will, probably... Doing both actually alerted me to an issue with pH in my tank. My pH was 8.2. Always 8.2. Before and after a change, 8.2. It was so boring, I stopped testing pH for awhile. (I do two 60-70% WC each week, one on Sun, one on Mon.)

Until one day, when I did the test _immediately _after a change, it was 7.6! Something came up and I had to do something else for about an hour, then I re-tested and it was 8.2 again. What I discovered was that my tap water is more like 7.4-7.6, and my big water changes were really pulling my pH down!

But by some magic, even with those large water changes, pH was rising back to 8.2 within 60-90 minutes. My fish never showed any sign of distress from it, no flashing to speak of, so I had no idea I had the problem. I wouldn't have known if I hadn't done the before and after testing.

I now use 2 teaspoons of api buffer max on my water changes, and the pH is back to 8.2 in more like 20 minutes in my 75g, which I imagine is easier on my fish...

(One other time, when I was medicating and I had removed my Purigen, frequent testing let me know that I had a nitrate spike.)

The point is that I wouldn't have known I had a problem otherwise. I also like to get my nitrates below 5ppm by the 2nd change, so testing before and after lets me verify that, because the nitrates "orange-y" colors between 10, 20 & 40 are so subtle. But when you have it below 5ppm, you can tell for sure. I'm saving up for a denitrator, myself.

I seldom test for ammonia or nitrite anymore. pH, kH, gH, nitrates before and after, and maybe every other week, phosphates. that's it for me.


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