Jason, I used to keep tanks and ponds with minimal testing, similar to you I used the pet-store to test my water. I had a mentor that sat down and started explaining keeping water to me, his saying was, To keep fish successfully, you must first learn to keep water. As I have learned over the years by doing my own testing and reading to learn how to keep water I have been far more successful in my fish keeping. I also learned one major thing, If someone tells you your water is fine, they probably don't really know what they are testing and reading as well. They only know that the test kit they are using is reading that they are in the OK zone. Do you really want to put the trust in your pond into some ones hands that really doesn't know what they are testing? There are many people on this site that do understand water and how it works, and how to test and tell you what those readings REALLY mean. I recommend doing one of two things, Personally I would get my own kits and do my own testing, BUT, if money is tight, at least get the store to test and write down the results and post them for one of us to look at and tell you what those readings mean. Since I have a little free time on my hands I would like to go a little further on this, Not only for you but for anyone else that doesn't test to go by.
Tests that I feel are essential to get done or have.
Ammonia, Nitrite, nitrate, KH, GH, PH and temperature.
So now that we know what to test what should these readings be in an established pond.
Ammonia should read 0 anything more than that and there is more waste being produced than the bacteria can break down, VERY DANGEROUS!
Nitrite should read 0 anything more means the ammonia is being broken down and there was a spike in ammonia in the last few days, Suspect over feeding, or a fish or other animal died in the pond. Not as dangerous but anything more than a 10ppmm reading really needs to seriously be looked at as finding out why!
Nitrate should read as low as possible, But a low reading means that the BIO in the filtration is keeping up with the waste being produced. If kept below 20ppm then it is really no harm to fish, and can be kept under control with plants and water changes, actually most koi and goldfish can live in nitrates as high as 60ppm but this extreme is NOT recommended.
KH, you really want to keep KH between 80ppm and 200ppm, This helps keep PH stable. Lower than 50ppm can cause extreme PH swings from day to night. I try and keep my ponds between 80-140ppm for my pond.
GH, this is the general hardness in a pond or water source. Knowing what it is out of the tap and watching to make sure it stays stable is the most important part of keeping Koi and Goldfish. Not critical in most ponds but it is critical for fish like discus or tetras in aquariums as they need low GH or African cichlids which need Hard water or high GH.
PH. In a pond stability is what's most important. Koi and Goldfish can handle PH of below 7.0 to 9.0, but the best reading is between 7.8-8.4, This is why KH is so important. If the KH is kept in the correct range the PH will stabilize in this range and will not move more than a few tenth's in a 24 hour period.
Temperature, Why do I Include this? They can't test it at Pet shop because it changes from the time you collect the water to the time you get it to the store. You have to check this at home, This is the first test most of us learn to test when it comes to pond keeping, why is it first? because it's the easiest to read and the cheapest test to buy. Why is so important? We can't control the temp, nature does and the pond is outdoors. BUT we can figure out when to feed, and how much, and what to feed when. In keeping Koi or high stocking rates this is extremely important, We never want to feed a pond when the water is below 50 degrees, Bio can't keep up with the waste. What about high temps? feeding when water is above 80 degrees increases the chance for oxygen depletion. above 90 and it's virtually uncontrollable to do large water changes if a problem occurs due to the fact that you will probably shock the fish from temperature changes in order to keep enough oxygen in the water to keep ammonia under control. Bio conversion does not break waste down as effectively from the lack of oxygen.
Of course there is more to keeping water, and fine tuning what you want or need in your particular pond. Koi keepers need to make finer tuning in their ponds in order to keep certain colors from fading. Such as adjusting hardness can effect certain colors in koi as well. Plants help remove nitrates, but noone has a formula to tell how many plants it takes to remove a particular amount of nitrates, so testing is important so you know when the plants can't keep up and when water changes are needed to help control. Learning the basics of water keeping and how and what to test for can REALLY help anyone that is serious about keeping their fish healthy. It also doesn't have to be expensive. You can pick up most of the test kits for around $10 each, or you can get a Master kit and the KH for about $40-$50 and that will last you close to a year maybe longer. What is water testing and keeping your fish healthy worth? For me that less than what it could cost me to replace 1 fish I own 60 valued at more than that, I had to take water testing more serious, I hope anyone that reads this post considers about how important and why testing is so important to take the time to learn and do.
Here is a Video of how much I feed my fish @ 3 times a day, Is it too much? Is it too little for summer? Is it the right amount? Thanks for your advice 
