Question about pH test kits

[An t-iasg]

I use the Wardley pH test kits. I have the high range and the low range kits. The high range kit says it's for saltwater or brackish. Does it just say that because SW and brackish need higher pH than freshwater? I'm using the high range test on my freshwater, and I wonder if it's accurate in FW.

When I use the low range kit, I get 7.4, but my water is darker blue than the 7.4 color chart, which makes me think it's higher than 7.4. When I use the high range kit, I get 7.6. So I'm wondering which reading is accurate. I think the 7.6 reading is probably more accurate, if the high range kit is accurate for freshwater.

 

[sweetsuvvyb]

Seawater does have a higher pH than than "pure water", but that doesn't meant that freshwater aquariums won't have a basic (alkaline) pH.

In a reagent-based test, I don't think it matters what the salt content is (As opposed to an electrode based test, which is based on the conductivity of the sample...a marine sample is drastically different than a FW sample here).

My pH hovers around 7.4...it tests the highest on the low-end pH, and the lowest on the high end. It's the same reagent, just with different dyes.

These tests are not the end-all and be-all of accurate pH measurement (they are far from it). They are best used as an estimator, and as a way to monitor change. Whether your water is 7.4 or 7.6 (or maybe 7.5! lol)...either is just fine.

 

[An t-iasg]

Hi Sweetsuvvyb,
They are the same reagent, with different dye -- that's good. I did wonder, as I was posting the question, does it really matter if it's 7.4 or 7.6? I thought of 7.5 too! Well, maybe it doesn't really matter, as I'm not going to try to manipulate my pH with chemicals anymore. But I think I need a reference number to try to keep the tank stable at, and like you said, to monitor change. So, while all the above pH's are fine, it's good to know that the high range test is reliable enough for FW! Thanks!

 

[captainGregor]

A little alkalinity is actually better for overall stability of the water. Acidic water is more prone to the PH swings. Do not use any chemicals to alter PH! You should not treat the PH but rather figure out what causes the problem. The process of decomposition increases acidity whereas something containing base elements in the water is causing alkalinity - like accident lime-based rock or something. Like a lot of people say - let it be high (or low) as long as it is stable. I totally freaked out when my new 55g cycling tank showed me 8.8 PH yesterday, and tap water is around 7.2. I went to bed, and this morning it was 7.6 as always. The morale - we make mistakes and tests are far from precise.