Yes, water changes should be done weekly. A good rule of thumb is 50% once a week for medium/full stocked tanks (sometimes more than that, depending on nitrAte readings.)
It doesn't make sense that you get 0 nitrAte readings. You shake not only the bottle #2 (it contains crystals in it, that have to be broken apart and put back into solution for the reagent to work) but also combine water+bottle #1, invert the tube 3-4 times, add drops #2 and shake for 60 seconds? If you have fish in the tank, and it's cycled, then nitrAtes are the end result, otherwise you will have ammonia or nitrIte readings present.
If you only do water changes once per month, I would imagine your nitrAte would read Dark Dark red, and it will probably take back to back water changes to get them down to a level that's suitable for fish. Even a 50% water change with nitrAtes at 200 will put them at ~100, which is still WAY too high, which would explain why you have seen no difference. Don't do more than 50% at a time, since doing that will shock the fish, and possibly lead to infection/death.
I don't think it's the rock. Granite is a very good rock to use, and if you soaked it for a week, I don't imagine anything is in it that will harm your fish.
It doesn't make sense that you get 0 nitrAte readings. You shake not only the bottle #2 (it contains crystals in it, that have to be broken apart and put back into solution for the reagent to work) but also combine water+bottle #1, invert the tube 3-4 times, add drops #2 and shake for 60 seconds? If you have fish in the tank, and it's cycled, then nitrAtes are the end result, otherwise you will have ammonia or nitrIte readings present.
If you only do water changes once per month, I would imagine your nitrAte would read Dark Dark red, and it will probably take back to back water changes to get them down to a level that's suitable for fish. Even a 50% water change with nitrAtes at 200 will put them at ~100, which is still WAY too high, which would explain why you have seen no difference. Don't do more than 50% at a time, since doing that will shock the fish, and possibly lead to infection/death.
I don't think it's the rock. Granite is a very good rock to use, and if you soaked it for a week, I don't imagine anything is in it that will harm your fish.
