weird test results

I have just been testing the water in my tank for various things and am amazed at just how different they are.. I have the TetraTest Laborett liquid test kit, and got these readings -

kh - 4
gh - 9
ph - 7.0
co2 - 13 (ok for my readings)

The last time I checked the water with this kit the ph was 7.5 so this was quite a change. I thought the ph was a bit low so checked it on my API Masterkit -

ph lower - 7.6
ph higher - between 7.4 and 7.8

It seems that I can pick any ph of my choice!! I am not sure now what reading I should take as Gospel and whether my ph is getting a bit dangerous, especially as I have had a couple of cory's die over the last few days

What test kits do you all use and have you ever had this sort of difference in your readings? I am not sure which one to go by now. I'm going to leave some tapwater overnight and do a test tomorrow just for interest.

I would appreciate some advice please

Well I always go by the API test kit as I've found it to be the most accurate. I did have the Nutrafin one before and there was too wide a scale in the results. Your pH results for the API test seem to correspond though in that a pH of 7.6 is between 7.4 and 7.8...so I would take that as the accurate one.

Thanks Mary, I dont have to rush out and buy the Sod Bicarb yet then!

Well with a KH of only 4, I'd still be inclined to do a weekly test. The KH in my goldfish tank was zero when I tested it on Friday...

Sometimes I wonder if it's better to liv in blissful ignorance

indeed DIana, I use the API test kit. My PH has stayed stable however I havent tested my water for probs over 1 month.

It's always worth testing the water every now and then, GD 'coz even in a fully cycled mature tank - things can sometimes go awry...

how often do you test your tanks Mary - do you still do them every week like a newbie

Ive got into the probably bad habit of checking about once a month but am thiking that I need to get my act together and do them at least twice a month if not more. What's the acceptable norm do you know?

I usually only check the ammonia, nitrite etc. if a fish dies. But I test the KH every week because I have very soft water and the KH drops every so often, requiring the addition of sodium bicarbonate to keep the pH stable.