2x 48w vs 1x 80w UV

theotherfishnoob · Jan 22, 2025

So i haven't got much space for a 80w 1meter long uv... I can have it at the back wall of the sump area but bulb change would be difficult and I'd have to pull the whole thing out to do it.

So if I had two smaller UV lights in series would I get the same effect as one 80w?

If so, id atleast be able to side mount it for easy bulb changes. If not.. well it's back of the wall or external mount (requires 10 90degree bends and a fair bit of vertical and horizontal pipes.. a bit of pressure loss there)

Goal: ich management
Tank: 1800x600x600 (6x2x2) 650L uk
return pump vectra m2

Quietman · Jan 23, 2025

I don't think UV filters work quite to same specs in series as the control has to do with exposure and time of exposure. That said, it's got to be pretty close if you have one then the other right after.

For a 180 gallon tank 80w is a bit overkill. You could get 180000 uwatt/cm2 at 400-500 gph on a 40w to 57w unit (plus or minus depending on exact wattage from manufacturer).

There are reasons to go big of course, like keeping high flow for algae and still getting protozoa coverage but if size is limitation, you may want to consider dedicated loop for UV with a variable speed pump and go much smaller with UV.

BryanM · Jan 23, 2025

I bought a 40w pentair for my tank, same size as yours.

The big benefit of running two UVs is that you could set one up for algae, and the other up for fish disease, these require different flow rates.

Quietman · Jan 24, 2025

BryanM said:
I bought a 40w pentair for my tank, same size as yours.

The big benefit of running two UVs is that you could set one up for algae, and the other up for fish disease, these require different flow rates.

The flow is based on providing the different exposure to UV to damage/destroy the different organisms. The flow ratings are just to support the exposure. High flow is usually to cycle through the tank for organisms that reproduce quickly as some bacteria can double in 20 min (that'll be the extreme end) and usually that's going to be 8x turnover at the lower exposure rate (30k uw/cm2). But you can have the high exposure rate for protozoa (90k-180k uw/cm2) if you have a higher wattage UV.

Depends on budget and set up. Some like one bigger UV and keep flow constant to always protect for both, similar to running two units on separate loops. Others will run one smaller UV but have a variable speed pump and adjust as needed. Currently I run an oversized UV at constant flow.

theotherfishnoob · Jan 24, 2025

I was just thinking I could run 2 smaller UV's at the same time one through the other, positioning them where maintenance is easy.

I'd be running the flow through them the same as I would have for the bigger UV. Technically speaking, you still get the same exposure time but with a tiny break in between.

The 2 smaller units at 48w equal to 96w.. more than 80w for the larger unit.

Both are deltec UV if anyone's familiar with them.

The 80w would let me do 1800lph with 3x turnover for ich.

I'm assuming I could achieve the same lph if not, slightly faster turnover (doesnt matter to me) and get the same results.

Is the logic correct here?

BryanM · Jan 24, 2025

theotherfishnoob said:
I was just thinking I could run 2 smaller UV's at the same time one through the other, positioning them where maintenance is easy.

I'd be running the flow through them the same as I would have for the bigger UV. Technically speaking, you still get the same exposure time but with a tiny break in between.

The 2 smaller units at 48w equal to 96w.. more than 80w for the larger unit.

Both are deltec UV if anyone's familiar with them.

The 80w would let me do 1800lph with 3x turnover for ich.

I'm assuming I could achieve the same lph if not, slightly faster turnover (doesnt matter to me) and get the same results.

Is the logic correct here?

Seems reasonable to me, if the water isn;t going back in to the. sump first I think your logic is sound.