Harlo, long time no post... There are a lot of newbie in Aq asking questions about test kit, so i will try my best to answer them here...
Test Strip VS Test Reagent (liquid)
For me, i will prefer liquid type as they are more accurate. those all in test strips are a disaster to read and the colour will change as it evaporates... darn headache to read the colours and compare the result in time
Expiry Date
All stuff has expiry dates...open your MATA (eyes) BIG BIG to check the box for one, if there is none...don't BUY.
Brands to choose
Personally, i find API brands the cheapest but also hardest to read. the colour change is very minor. I am using SERA and PRODAC brand test kits. So far so good.
Types of Test kits that i think is a must have
Cycling of aquarium
These 3 test kits above is for checking whether your tank has sufficient Beneficial Bacteria (BB) for keeping the water parameters stable.
These test kits is generally to know the poisonous stuff in you tank is absorbed by plant or whether an emergency wc is required. After cycling, i only test for nitrate. Too much nitrate will cause algae bloom. Ammonia is to check during sudden death....well, i only test once a month... so i still have at least 75% of the test liquid.
More info
http://theplantedtankblog.blogspot.sg/2012/05/nitrogen-cycle-cycling-of-tank.html
General Well Being
This is to check the the amount of chlorine in the water. There were feedbacks in AQ members from certain part of sg ( new development) has unusual amount of chlorine in their tap water.. well i skipped this test kit as i think my area is still ok and my OF anti chlorine has not fail me so far.
Note: May need to check if there is unusual death after WC
Fishes and shrimps lived in certain habitat of water, hobbyist are trying to simulate the environment they stay in naturally, thus a PH test kit is required. However, fish are generally more tolerant as long conditions are not too extreme. e.g neon tetra like PH 6, but if you throw them into PH 9 waters... they will be sick/die in no time..
Shrimp Keeping
This is to test General Hardness of water. In lay-man term... all the elements of water. Calcium, magnesium, potassium etc are lump into a category GH.
Certain shrimps need certain GH to MOLT ( shed their outer skeleton and grow new shell).
if high water has high GH, the shell will harden too fast and shrimp will not be able to grow in time...will cause death
If the water has low GH, the shell will harden too slow and shrimp will die too...
For info on shrimps i have and the condition i keep them in
http://theplantedtankblog.blogspot.sg/2012/08/hardy-shrimpsto-share.html
Where to buy test kits?
Hospital? hardware shop?
lol... LFS of course...
which LFS?
Read this, you can find the answer below
http://theplantedtankblog.blogspot.sg/2013/01/starting-new-tank-happy-new-yeartank.html
What about other test kits i saw in LFS that are not stated here?
Well there are a lot of test kits in the world, but i don't think you will need them unless you are darn serious about the water parameter or you loves lab work...lol
INFO: some of the test kits are actually for reef keepers...well feel free to explore... i don't have the money to explore....lol