I just replaced my Metal Halide bulbs last week because they were fatigued, but now I have a daily issue with the formation of green algae on the glass.

Light schedule

2-54 watt actinic 8am till 8 pm

2 150 watt 10K metal halide 2pm till 7pm

I guess I should say that the old MH's were 150 watt 14K a bit more "Blue" the 10K that I replaced them are very white.

Anyone have a suggestion as to how to control this algae problem?

I noticed the 10K's do create more algae on the glass.  I just switched from 10K's to 14K's and have less algae growing for some reason, the older my 10K's got the worse the algae got.  The cheaper bulbs from ebay may have a lower par rating also which will create some growth also.

You can try if you do not have already a phosban reactor with GFO in it, or a refugium with some macro algae.  Those may help with some undesirable algae but it will not completely eliminate the scum that grows on the glass.  Invest in a good mag float.

woodycb said :

I noticed the 10K's do create more algae on the glass.  I just switched from 10K's to 14K's and have less algae growing for some reason, the older my 10K's got the worse the algae got.  The cheaper bulbs from ebay may have a lower par rating also which will create some growth also.

You can try if you do not have already a phosban reactor with GFO in it, or a refugium with some macro algae.  Those may help with some undesirable algae but it will not completely eliminate the scum that grows on the glass.  Invest in a good mag float.

you are so right. I started with 10k because everyone said that is best for coral growth. After fighting the algae for almost 8 months, I switched to 14k. Never had algae problem after that. I guess it's a trade off...