I thought it might be an idea to compare the accuracy of liquid tests to test strips as this issue comes up so often.

I've done some comparisons today using water straight from my tap for all the tests, plus an assortment of mixes of ammonia and water. I was also able to compare the results in some cases to the Water Quality Report for my supplier, and for pH and TDS (which can be converted to gH) with results from my own calibrated electronic meters.

Obviously, because this is hardly scientific or fully controlled due to being done by a non-scientist in a domestic environment the results are a guide only, and for that reason I won't name the manufacturers of the tests used.

The first test was for ammonia using tap water. My water supplier reports 0.01 ammonium, the liquid test reported 0.25 and the test strip showed 0. In this case I believe the test strip was most accurate.

Nitrite testing was not much of a test as I have none to test with, but my water supplier reports .006 and both the liquid test and the test strip report 0.

pH is shown as 6.9 on my water supplier's site. My electronic pH meter reports pH 7, the liquid test also reports 7 and the test strip shows a colour between 6.8 and 7.2. As it has no separate indication for pH7, it appears to be correct, but in this case with nothing to compare it to, a judgement about which colour it is closest to is needed and so it is less precise.

Nitrate is shown as 40ppm on my water supplier's site and tested the same (40ppm) with the liquid test. Again with the test strips there are large jumps between readable levels so as the colour indicated fell between those for 25 and 50ppm, it is certainly in the right area, but the broadness of that range between colours makes it impossible to be precise.

kH could only be checked with the two tests. It isn't shown on the supplier's site and I have no other means of testing. The liquid test showed 6dkH, and the test strip showed just over 100ppm (which is 5.6 dkH, therefore it was probably indicating 6) - again this agreed with the liquid test, but as the next colour segment was 180 (10dkH), accuracy between levels is not practically possible.

gH on my water supplier's site is 11dgH, the liquid test showed 11dgH, my TDS meter read 198 ppm (also 11dgH) and the test strip gave a reading of 200ppm (11dgH again). All tests essentially agreed.

Finally I mixed a solution of household ammonia and water at 5ppm. It was tested at that strength and by further dilution at 2ppm, 1ppm and 0.5 ppm. In all instances the liquid test and the test srip agreed and measured correctly.

My conclusion from this is that the liquid tests and test srips were both accurate within their own design. Because the gap between levels at identifiable colours was quite large for some parameters on the test strips this made them less precise, but still able to give a good general idea. The ammonia, pH and gH tests produced good results in comparison with the liquid tests.

As a quick check when normal parameters are known, the test strips can be a useful tool, but I wouldn't use them to cycle a tank as they are too wide-ranging, nor would I use them to establish which fish to keep in my water.

Im actually very surprised your test strips did so well... you must have a faulty one.

In all my experience, both first and second hand, test strips are not at all reliable and should not be used.

I was very surprised. I've never used test strips before, but knew the reputation they have for inaccuracy. I only came back to fishkeeping a couple of years ago and when I last kept freshwater fish testing just wasn't done - it was still all fish-in cycling the old school way (a couple of Platys who had to take their chances ). I'd come across test kits during a short time keeping marine fish in the early 90s, but used liquid tests then, so on coming back to the hobby through circumstance (the big plec below was being threatened with the toilet), I used liquid tests from the off.

However, I must point out that the strips I used were made by a British manufacturer and have only been on the market a short time so maybe they're an improvement on other brands?

It's also clear that if you don't read them one minute from dipping, the results do change quite rapidly so they need to be used absolutley as directed. I gather another problem with all test strips is moisture causing readings to be off, even from the atmosphere, so they need to be kept in their sealed container and I would imagine with repeat opening they may deteriorate. On that basis I'd say they should be used pretty quickly once opened.

The other thing is that I am very well aware of what my water readings are so that may have assisted in my interpretation of the results, but even so, they did very much better than expected.

I wouldn't describe them as inaccurate, probably "less sensitive" than a liquid test is a better description and I wouldn't want to rely on them for precision, but then I won't do that for pH or TDS with liquid tests either - partly for speed.

I would still recommend liquid tests especially for anyone starting up as in the early days more precise testing is better, particularly when choosing fish, cycling, and monitoring a new tank. For someone familiar with their tanks these could have a place as a very quick check which can be investigated further if anything odd shows up.

That's really interesting Noodle, thanks for doing that and posting about it A lot of people are critical of dip tests but I do wonder how much is 'word of mouth' and how much is direct experience. Interesting that BG has both to speak from, maybe the dip tests have improved recently, if you've not used them for a while perhaps things are better now? I've only ever tried a dip test for nitrate and it's usually about in the same area as my liquid one. But then I've tried various liquid ones for nitrate and got very different results from three different manufacturers.

Maybe there's something in how you actually do the test and the context you're using it in. If you're using a dip test for a quick check to see if things are what you expect ('maintenance' as it were) that sounds reasonable, but where greater accuracy is concerned (initial set up and cycling) it sounds like liquid ones are the better option. Horses for courses perhaps

EIA - crossed with you there Noodle!

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Hmmm... good points.


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More good points. I've had different results from different manufacturers for most of the usual tests. I used to use Waterlife until they made the pH chart difficult to read. Now I use API.

I have some test strips and in my case they agree with my liquid API test for ammonia, tell me there is no nitrite when my liquid test says 0.25 and tell me I have a pH of less than or equal to 6.4 whereas my liquid test says 7.6 or above.

So I trust the ammonia one bur not the others.

So anyone with dip tests might benefit from keeping a sachet of some kind of hygroscopic crystals in with them? Unless they touch and react with it? I wonder what would be safe ...

E.g these

I would assume there's a possibility of some interaction as I would think the manufacturers would include a dessicant gel if it solved the problem. They tend to be clear that the test pads shouldn't come into contact with anything (including fingers) so perhaps that's what they don't use them?

When I'm feeling rich I may buy a pack of one of the better known strips and repeat the experiment as it would be interesting to know if these new ones I've tested are better or not.

So where did the wisdom come from that test strips are completely useless? Is it just another thing that gets repeated all the time without any evidence to back it up, like the goldfish organs keep growing and cause them agony if they're kept in a small tank urban myth? I've repeated the 'test strips aren't accurate' thing myself without trying to verify it just because everyone else says it, it's a very successful meme.

Just shows, we need to be careful not to believe something just because everyone on intenet forums tells us it's true. No wonder us newbies always get so confused from all the conflicting advice we recieve...