04-11-2011, 01:49 AM
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Fish are not meant to be in 'sterile' water, it can nerve bee completely sterile, but its much deader then natural water. If everyone used UV our fish would end up with weak immune systems. The immune system is a "use it or lose it" deal. We see this with some farmed fish, that are raised in medicated water. As soon as you remove the medication, you often get a die off from disease. Thus those with the best resistance to sickness are usually the ones that are not sheltered from it. The act of getting a disease is a sign of something wrong. Just because say ich was introduced to a tank, doesn't mean the fish will get it. If they are stressed or in a weakened state then yeah they will get infected real fast. If fish is healthy, happy, and unstressed they can fight off diseases quite well. The whole point of the slime coat is for protection.
Any disease showing up in a tank raises a number of questions for me at least. The problem is not the disease itself, but a sign of another problem. Why did disease show up?.. Where fish stressed in the tank? Did new fish bring it in? If so then these are your real source of the problem not the disease itself. Perhaps the solution is a quarantine tank to better screen new fish.
Many people use UV for algae control in response to a algae bloom or green water. The problem may not be the algae for example, but high phosphates or organics in their water, which cause the algae. Using UV kills the algae, it doesn't change that the phosphates are still high. Its simply masking the underlying problem.
UV works both ways. It kills harmful microbes as well as completely harmless ones. Some may not care about this at all. I prefer to leave fish to their own devices. With UV there is a pretty good guarantee I would never find any fry from my tetras unless I raised them intentionally. Its not common but occasionally a 1/4" tetra fry just shows up in my main tanks. Just a lucky one that avoided the rainbows and found enough live food to eat on his own.