Test kits

[Aquafreak]

I took some water with a set amout of KNO3 in it to the LFS for testing and I noticed that some test kits just do not work with particular DIY ferts, eg. the Hagen Nitrate didn't show anything for the KNO3. Now it got me thinking whether my KH test kit is showing proper results, I have a CO2 indicator in the tank and I read that if you add fleet, the results could be altered and therefore not showing proper readings. If this is the case with a combination of an improper test kit, I'd be misreading the amount of CO2 in the tank.
Anyone know if KH needs good test kits or particular brands? Or is it like pH kits, most brands will work?

[inxs]

IMO ph tests have been around for a while and have been improved to the point where even cheaper ones work well.

I haven't heard of any problems with KH tests - I think you could test it by disolving some bakingsoda in water to make sure you get a high read and testing some RO/distilled to make sure it registers low or none.

Testkits do have a shelf life and older ones may not give accurate results.

NO3 tests , especially the low range which is the most useful for planted tanks, need to be good which usually means more expensive. I use the Saliferts which is rated very good but cheaper than LaMotte . If you are really serious you should try to find a good one - IMO the NO3 kit is the one to invest in a good one. If you want to spend on PH - get a probe.

As I said before , even with a good testkit, it is vital to shake the ingredients well before use and letting it sit for a while (overnight) will also help.

[djlen]

I've never heard of PO4 affecting the readings, CO2 or any others.
Having driftwood or African Root in the tank will definitely affect your pH/kH reading. My pH in all my tanks was very low. So low that according to Chuck's Chart I should have had over 60ppm/CO2 in the tank. The fish, at that reading(CO2) should have been gasping at the surface at best and dead at worst. I found out that the African Root I had in the tank was causing a false reading when I tested for CO2.
I use Aquarium Pharmaceuticals(pH & nitrates), and Hagen's (PO4) and they are, IMO pretty accurate.
As inxs says there are better test kits available, and a pH probe is a good item to have.
When in doubt about a kit I put an excess amount of the nutrient being tested for in a small amount of water and test that. If it comes up low there's a problem with the test kit.
One thing about testing for nitrates with the AP kit. When they say shake the #2 bottle for 30 secs. they mean it. I shake for longer than that, because it makes a big difference in the results. Also it must be given the entire 5 mins. for the color in the tube to develop.
Len

[Aquafreak]

I have a red sea NO3 test kit, seems to do a good job, I also have a pinpoint ph probe, just been wondering about the kH because I measure my co2 with it, don't want huge false readings is all.

thanks for reply

[mogurnda]

PO4 is a buffer just like CO2. If you are using an acid titration test kit to measure your alkalinity, you need to add enough acid to saturate both CO2 and PO4 reserves. If you have a LOT of PO4, this could be an issue, but usually isn't for most of us.