I've been battling some GHA issues lately and have been wondering if my lights may be to blame. My nitrates are nearly undetectable and temp has been at 78 (fluctuates from 77-79) and my salinity stays stable at 1.025 and I have an auto top off so it really never changes. I keep my lights on for 10 hrs a day, but had them at 12 hrs during the summer time. I'm probably about to cut them back some more. I do have pretty low flow, but have had the same flow for years with no real issues.

I'm thinking that I might need to get new bulbs but when I bought my T-5's I was told that unlike MH and PC they would hold thier spectrum until they burned out. Is this true? They will actually be 2 years old in January so if they do shift I would be willing to bet that they are BAAAAAAAD!!!!!

I will probably be increasing my flow and reducing my light cycle for now, but if anyone has any info on the lifespan of T-5's please let me know. This is getting pretty bad and I don't want to drop $100 on bulbs if I don't have to.

bump...

I've tried searching but have found people saying 6 months (pretty sure that's wrong) and people saying a few years.

When I purchased my 4 bulb T5 fixtire from Hellolights ( which is still in a box in my basement ) I had the same question. I phoned their Cust Service line - and was told they could last about 18 months before needing replacement - but that I should stagger replacement of the bulbs - b/c they do dim over time rather than going out all at once.

I change mine out yearly. But I have heard 12-18months. Probably depends on your photopeiod too. I only run mine 8 hours daily. And still change out yearly just to be safe.

good luck, Mike

hmm... Might have to spring for some new bulbs then.

I would recommend restricting your lighting to 8 hours (10 hours max) a day to cut down on unnecessary algal growth.

Florescent bulbs tend to slowly, but steadily, lose brightness over the first couple months, then tend to 'stabilize' with a much reduced intensity dropage. My 12" regular T5 bulbs lost just over 30% of their original intensity after about 8 months. I suspect that I could have used them for another 8 months and the intensity wouldn't have dropped much more, but the spectrum would have started to shift. That's what is happening with your 2 year old bulbs and the algae will take advantage of the shifted wavelengths.

I change mine at 6 months, but only because I need as much intensity as I can get out of my 12" T5s.

12-18 months is usually when I changed mine. What spectrum bulbs are you using? I prefered an 8 hour light cycle to keep algae issues down, actinics for 1 hour, all ights for 6 more hours, then actinics for 1 last hour...

Well I run a 10K and an actinic, but they are not able to be put on separate timers.

I might end up getting a second fixture though that can run my actinics. I've built up some credit at the LFS and might get just 2 new bulbs, or maybe 2 new bulbs plus another 2X T-5 setup.

It's best to change the bulbs, if only to get ones with better spectrums than just "10000K" and "actinic". See the T5HO information thread for more info on bulb selection.

I change mine every 12 months.

The thing about FL lamps that has the greatest affect on a tank is not the change in intensity, but the shift in the spectrum. As the lamps age (really any lamp) the light spectrum from the lamps shift. You can't see it but it's there. No mater what type of lighting, I'd change the lamps between 9 - 12 months.

I change mine out every 9months max. Mine are overdriven though so that changes it a bit.