175 watt mh with 20k bulb question.

[ElectroTT]

hey all. i currently have a 175 watt mh fixture with a 10k bulb supplemented by 2x36 watt actinics. both actinics are blue. im thinking about getting a 20k bulb. what should i do with the 2 blue actinics? should i change the bulbs for whites? or keep 1 blue bulb and change 1 bulb for a white bulb? confused here. do u guys think it would be unhealthy to have a 20k bulb and 2 blue actinics? this is for a 29g tank. been set up for about 2 years now.

[Undertheradar]

The color doesnt concern me...but the overall output does. 175watt bulbs have dismal outputs. How low? Here are the results from some independent PAR tests done on a new line of 20,000K bulbs.

 

"For comparison a 175 SE - 180, 250 SE 400,400w SE 1100, 250w DE 1000 to 1200, and 1000wSE over 2000 !!!!"

 

The only bulbs that they didnt test were the 150wattDE and the 70wattDE...from experience I can tell you that the 150DE would be about 200 PAR, and a 70wattDE about 100.

 

Also, as a rule of thumb, 20,000K bulbs put out half as much as their 10,000K counterparts. So a 400wattSE at 20,000K could almost be outperformed by a 250wattSE at 10,000K.

 

What does this mean? You are already at the lower end of the spectrum as far as outputs go simply because of the 175wattSE bulb. Cutting your current PAR in half would not be advisable on a 29gallon. The minimum wattage I would suggest for a 20,000K on a 29gallon would be a 250wattSE...if not a DE just to be sure.