They sell it in walmart for 3-8 buxs in fish section, usualy have ph uper and downer there aswell
There are many different chemicals that can be used to detect the ph of any liquid. For example, pool test kits use phenol red, which only has a ph range of 6.8 - 8.8
Which means if you use a pool ph text kit, and your ph is 5.5, you will not know it, because phenol red does not accurately reveal ph in that range.
Thats why it is important to get the right test solution. You need something with a wide ph range.
Its also important to remember that using nutes or molasses
will severely drop the ph of your water. If you use nutrients without a ph kit, youre destined to fail.
Good luck - bigtomatofarmer