View Full Version : Eheim UV 500 sterilizer

01/29/2014, 08:06 AM
Hi, been thinking about getting one of these for my 14g (roughly 50L) nano to control algae (diatoms) but have a technical question for the experts 😉

The unit states that it requires a flow rate of 400L/sec in order to kill bacteria and 800L/sec to control algae. Basically I guess this has to do with how long the water is in contact with the UV light. The lower the flow rate the more actively it will kill stuff.

So far so good. I should also mention that on the box it is stated that the unit works in tanks from 300L to 500L (yep, that is 10x the size of mine 😳).

Another point is that this would be placed in line on the return of my external filter unit which has a flow rate of 1250L/h...

This is where it gets complicated. My understanding is that because of the higher flow rate (1250vs800) the water will run through the UV some 50% faster than the recommended rate. In other words, it will spend only 67% of the time each time it passes through the UV. As such I argued that it would not be effective.

However, my LFS argued that it would actually be even more effective, because even though the water would be going through the UV 50% faster than the recommended rate! given the small size of the tank it will be going through the filter almost 28 times per hour, whereas in a 400L tank with a 800 flow rate it would only go through it 2x. So at the end of the day, in my case the water is actually going to have a lot more contact with the UV...

This is where I would like your input and expertise: is the LFS correct or not, because it does not matter how many times it passes through the filter but actually how long it stays in contact with the UV continuously on each pass?

I am sorry for the long post but if anyone can shed some light I would greatly appreciate it!

Kind regards