I've had them for 3 weeks, purchased from LFS. I have a 20 gal tank running since November, all readings are good, 0 ammo; 0 trite, 20 trate, 7.2 PH. I now have 2 platies, 3 neons and had 2 danios, but gave them away because they were too hyper. Just lost an albino catfish I only had for 2 weeks. :sad He showed no symptoms other than laying on bottom of tank for days.