Knowing Kh is important, but more of a one-and-done thing. The liquid ones due expire, so unless you're going to be using it a lot (either in the tank or because, like me, you will probably test other things for fun) a smaller test amount (such as strips) will work just to get baselines.Archaea said:KH and pH are inter-related. If KH falls below about 4 degrees hardness, there is a risk of what is known as a 'pH crash'. This is when the pH takes a nose-dive and drops to a very low level. If it falls much below pH6, this can kill off the beneficial bacteria in your setup. And ammonia/nitrite is likely to be a problem. So, knowing the water KH is very wise. GH is a measure of water hardness. Some fish prefer soft water, others prefer hard water. You can get this information for each fish species from many places on the internet. I use Seriously Fish.