Hi all!! I have never tested my water since setting up my tank I know really bad. We have 1 gold severum, 2 angels that have just laid eggs, 5 dollars all happy swimming around very active. Today we purchased a bristlenosed catfish acclimatised as we did all our other fish we happily went to the bottom of the tank started munching on brown algae. Then after a few hours he was on his side still breathing. Googled this lots of people say it's normal and they have had the same. Also when buying him we bought a JBL 6 in 1 test strip. We used this after he went a bit funny. According to this test everything was ok apart from nitrites and nitrates were through the roof off the chart on the colour indicator. Over 500 on one and over 10 on the other. Tonight we have done one 50% water change and agitated the gravel to release all the and sucked up with a hose pipe and still not difference in test and one 75% water change still no difference in test. All fish still happy and swimming other than the bristlenosed which I think might have possibly just died as I'm writing this. With readings this high shouldn't everything in the tank be dead? I have attached a few pics left to right on test stick is before/during/after I can't really see any difference. What am I doing wrong?