Additional info about test chemicals.
This was from a previous post on the low-tech forum:
I bought a KH and GH API test set in January 2008 at the only non-chain LFS of any size in the area. There seemed to be a lot of customers all the time. When I got home and tried testing the water, I could not get any readings after a whole bunch of drops being added. I tried tap water and got the same results. I contacted API via e-mail and received a quick reply from them that was most informative. They told me how to read the code on the bottles, like 56A0107 means product 56A and bottled in January 2007. When I looked at the test bottles, they were of the year 2000 vintage, eight years old. The store took them back without question.
So if some of your tests are not too accurate, you may want to at least check the product date before reaching a final decision. I would ecpect that other chemical manufacturers use a marking system as well. You may want to open the package while you are still at the store if you are purchasing chemicals.
The following was received from API:
"Pond Care Wide Range pH, Ammonia, High Range pH, Nitrate, Phosphate, Copper, Calcium and GH all last for three years. Nitrite and KH will last for four years. Freshwater pH (low range) and Pond Care Salt Level will last for five years. I would not use or trust these kits after they have expired."
The last sentence was their statement.