We are Henan Shondunn EP TECH Co., Ltd, located at Shangqiu City, Henan Province, China(Mainland). We produce water quality tester(tds meter, ph meter, water electrolyzer etc), ro membrane(50-600gpd , 4040, 8040) and ro system by ourselves.We are not fool and stupid. If our quality not good, we can't do business long time. If we are not responsible for our product, that means you will not order again, we only can make money one time.Do you agree? So you no need worry, our products are good quality, we are also responsible for our products. You have my word.