UV sterilizer questions

[seancj]

Hello all.
I have a 15 watt and a 25 watt UV sterilizer at my disposal. These are used units so I don't have any instructions with them. They both do have new bulbs though which is nice. I purchsased these with the main function of helping control the dreaded algae blooms and green water issues.
Not sure which one to use.
My tank is 240 gallons, but probably only holding about 200 gallons due to sand and rock displacement.
I have added 20 3" pots of HC and another 8 small plants and plan on adding about 100 tetras in a few weeks. A few months down the road I may add another 50 tetras and eventually between 3 to 5 discus.
Would the 15 watt unit be able to handle this size tank/bioload, or should I go with the 25 watt unit?
Would it be enough to control algae blooms?
What gph should I push through the UV to be most effective?
Thank you for the help.

[grantbudd74]

I have an 18w on a 600l tank and its not doing anything to control algae but I would go with the larger one as the stronger the bulb wattage and also the larger the unit the less the flow rate will be slowed as the internal chamber will be larger.

My understanding is algae is only an issue if your nutrient, light or Co2 levels are out of range so do your research and try a dosing calculator to get it right from the start.

Have fun with it all but make sure you have taps to shut off the water from your pump if you need to replace the bulb to prevent water from leaking all over the place.

[Disgirl]

I use a 25 watt UV sterilizer on my 1800 gal Koi pond and it keeps the water crystal clear so the smaller one should work fine for your tank. But as I understand it, the UV is for the pea soup algae floating in the water. Does your tank have pea soup looking algae in the water? If not then you don't really need it. If you do use it then you need to make sure the water doesn't go through the chamber too fast.
Barb:)

[seancj]

Thank you for the replies so far.
Unfortunately, I do have the dreaded 'green water' right now and its making me crazy.
My HC was wasting away and some of my other stem plants were dieing off too, so I added the recommended dose of Flourish and Flourish Excel as well as the Seachem plant tabs at the base of all plants.
I hope to hook up the UV this weekend and see if it makes any difference.
What would be the best media to add to my Fluval FX5 to get rid of the green water more quickly?
Thanks again.

[Disgirl]

Well, for the green water the really best things are: less light, less ferts (may have too much in the tank) more wc's if you can and if those don't work then the UV will do the job. I have had the exact same prob. with my Koi pond and it was the UV that finally did the job. No type of filtering media in my huge filter did any good. I am thinking the same things apply to a tank. The microscopic algae just goes right through any filtering media. The UV light will kill the algae and the filter will catch the dead algae. Good luck!
Barb :)

[Dutch dude]

The base of green water problems is often related to lots of nitrates or phosphates (from fertilizers?) and also light intensity and color. Plants can outcompete algea for absorption of nutrients but you need to add fast growing plants like Egeria densa. Very cheap and handle low and high temps and can grow up to 8 inch in one week. So Egeria can help you to lower the nitrate and phosphate levels. If you find the reason why you have green water you find the cure to get ride of it. Solving the problem by creating a better balance between plants, light and nutrition will benefit your tank long term.