How to know if you have too much light?


I am (slowly) coming to the conclusion that I may have put too much light on my tank. So I moved my light higher and it is currently 9 inches off the water. How will I know if it needs to go higher or lower, and when will those signs appear? I picked the magic number of 9 inches because that was what a survey found.

I use a 48 inch ATI light with 6 t5 54 watt bulbs. Currently, I use 3 Blue+, 2 Coral+ and a Purple, all ATI. I used to put the lights about 4 inches from the water of a standard 75 (48x18x20?). A friend gave me a pavona and a lobophelia, which both lived in a 55 gal with 2 150 watt halogen lights (not changed in years), and in yellow water. The tank was rarely feed. Corals were extended and begging for food. When I put them in my tank, medium height, the pavona died in a week. The lobo was on the sand but stopped being puffy. Hard to think they starved as I least fed my tank daily! It is still alive. I put it in the back corner, and more recently to position more shaded and less water flow. I have tried acans several times which are puffy in the shop, but shrink and wither in my tank. I had never considered that I had too much light. I do run carbon and a protein skimmer with a refugium. Tank water is clear. I try to keep CA at 440 and Alk at 8.5, but clam seems to consume alot - doser has to be adjusted often. Mag at 1350. I changed 20 gallons every 4-6 weeks. Phosphates test at .02 to 0 with Hanna. Refugium has lots of calpera growing like crazy. There happens to be an algae in the fuge too, but will post on that separately. I export a 12 oz cup a week - at least.

Another sign is that the little arms on my zoanthids are getting shorter and smaller. The iridescent toad stool tentacles are also shorter. But the zoanthids and toads under rocks are bigger with longer arms. With the lights up higher, the arms seems to have gotten longer. I also have a dersa clam on the sand which is rapidly growing and happy as a, well, clam, I guess. *Where did that expression come from - they just sit there!

On the other hand, I used to have a very large toad stool and frogspawn that seemed to not mind the light (toad removed, and with the poison gone, the frogspawn deteriorated and died. I had both for over 8 years. I used to have a lot of SPS, but everything crashed about 2 years ago (assumed death was caused by large toad). Now, all test SPS die within a month. No idea why. The general thought was that I wasn't feeding the fish (corals) enough, so fish feeding has increased to 1 cube a day, sometimes coral dust, sometimes extra, all for a tang, flame angle, 2 clowns, and 2 pj fish. Clowns are breeding. PJs used too.

So back to the question, how do I keep that lobo alive? How do I know when I have too much light or too little light. I have never used a PAR meter? A little frustrating as I want to stock up again, but not watch it died.

thanks in advance for reading (at least some) of the post.

Andy V

Well-Known Member
BRS Member
You've got a lot of information in there, but to answer the question in the thread know for certain by measuring with a PAR meter. A less certain method is comparing your lights to others having success.

What I can tell you with 99.9% confidence is that you DO NOT have too much light. I have the same exact light, at the same exact height. Only difference is I run 4 Blue Plus, a Coral Plus, and a Purple Plus.

I have measured my PAR a few times now. With the sensor just underneath (like 1/8th of an inch) the water, I get 280 PAR. This is nowhere near being too high. It is basically in the sweet spot. 3-4 inches below the water it's already dropped to 200 - already in the lower range. I'll skip everything in between, but at the bottom of my 24" high tank, the PAR is 70.

Don't take this to mean your lights are too low. I have some beautifully colored corals, including SPS growing on the sand, although most of the SPS are in PAR in the 100-200 range. Many people would think this was low PAR.

The likelihood of your problems being too much light is near zero. It's possible you don't have enough, but I think you have other problems.


i was even thinking that there may be some sort of bacterial load causing some issues. I will post a few pictures tonight.

Upcoming Events

Zoom Tour of Joker and Slombari's Reef Tanks June 9th @ 7PM