So 2 nights ago I found that my Pleco had died, and from some reason my water temp had gone u to almost 80 degrees....there were also white fuzzies. Accumulated on some uneaten food floating around my tank. I immediately did a 50% water change and turned down my heater setting. The next morning one of my 2 swordtails had developed whitish gray fussiest all over him and was very lethargic. So I went to people depot after researching online that he probably had tail rot, also known as coloumnais....the store owner was there and recommended that I try "fungus guard" mare by tetra. This illness is highly contagious and I was advised to treat my whole tank Prior to treating, I checked my Ph, nitrate, and ammonia levels, everything was where it should be and my tank temp had leveled off at about 74 degrees. So I followed the package instructions...removed the carbon insert from my filter and put 3 tablets into my, 30 gallon, tank. The next morning I wake up to fine my 3-3 year old parrot fish have all died! I called pet depot and told them what happened l, they told me to call tetra. I called tetra and described what happened.....they have no explanation why my fish died......I got no apology...no offer to reimburse me for the product.....and am now out over $120.00 in fish losses .... Do not use this product, the company takes no responsibility for it! I have been keeping fish tanks for almost 20 years and will never buy another tetra product again.