As hopefully everyone knows UVS has a large amount of pros but then again has a very large amount of cons. Some of the cons seem kinda not true. So here i thought we could differentiate fact from myth on them.
Does it really oxidize some nutrients, i mean it doesnt work on the basis of ionization.....
Cleans the water too well
Kills pods (i really HIGHLY doubt this, i think it just kills phytoplankton that the pods feed off of)
I think this is one where you have to be a little careful with specific words:
UV *itself* won't have much of an impact on nutrient reduction, nor will it *kill* macro-bacteria or larger, multi-cell organisims.
UV WILL, however, generate small lamps of ozone ( another name for a UV lamp is germicidal lamp, which was the first generation system hobbiests could use to generate ozone. ( if you want, I can dig out the reaction, it's fairly long, so I'm not going hunting if no one wants it.) Anywho, even though there is no direct ionization from an electrical discharge, water + UV = a little bit of ozone. Note the "little bit" phrase. It's nothing like as efficient as a corona discharge system, especially with only a few tens of watts. Seriously less efficient.
Ozone will do some useful stuff with nutrients:
1) Ozone will bind to nitrite to form nitrate ( no2 + O3 -> NO3 + 02 ) ( this is actually quite cool, as this is a very rapid reaction, as long as there is spare o3, it will ALWAYS reduce the NO2, which is good for us + if you do it in a glass beaker, it glows green!)
2) carry out reductions on various harmful salts and compunds. In general, reductions = safe chemicals
UV will also not "kill" multi-celluar creatures directly. ( at least not in the doses we use, would be different if you were using KW's, rather than 20-30 Watts ) It does not have death ray powers. It *will* mess up their DNA, and it may cause sterility or inhibit asexual reproduction. This will mean that there is a reduced ( although not eliminated) ability for these organisms to reproduce. Therefore, you will get a downward trend in their numbers.
Don't forget that there will always be new organisms entering your tank, from food, your hands, the air itself, so you can never eliminate them. Which is good, the fish, just like humans, need SOME level of resistance in their bodies, or some new disease will come and wipe them out.
UV will also have a similar effect on biological green matter ( algae etc ) as it does in ponds. Koi keepers use UV to clarify the water. This works because the UV causes cellular disruption and also adds a slight charge onto the cell membranes ( becuase of the ozone - 03 breaks down to 02 + O, the O is a free radical that id DESPERATE to give it's electrons away or steal some for itself, this causes, essentially, a static charge. ( really crude description ).)
The upshot of this is that the single celled algae ( which is difficult to mechanically filter ) will more easily form clumops, which IS capturable with a mechanical filter, or skimmer.
Hope this helps
Steve
