Metal Halide distance from water?

[mrkookm]

I am trying to create a not so 'high light' setup for my plants as I am somewhat new at this and thought I was doing the right thing with my current lighting choice. but as I read the forums more I am soon realizing that I might have a little too much.

I have 2 x 175watt, XM 10k MH with Lumenarc III Mini reflectors over my 90g (48lx18wx24h) and currently have it mounted so that from the bottom of the bulb to the surface of the water it is 19", Is this distance ok for what I'm trying to accomplish?

To give an idea of how some of my plants are reacting to my 'current intensity' ; my HM in the foreground still pearls alot, Rotala Round is growing sideways, Pogostemon stellatus 'Broad Leaf' (6" tall from substrate) pearls continueously very tiny bubbles from a damaged leaf, Pogostemon yatabeanus (5-6") gives a bubble every 7-8 seconds and my Ludwigia's sp. 'Cuba' ( 7" tall) is growing new leaves that are pinkish redish.

I do want good growth but 'not too slow' . CO2 via misting is at 30ppm per my DC and I'm also following diligently for 3weeks now this routine (tank3) _Dosing Regime's_ - The Planted Tank Forum


Any info will be appreciated...........

 

[VaughnH]

The watts per gallon values we generally talk about are for AH Supply type setups, with the bulbs/reflectors only a few inches above the water. When you use MH bulbs, located much further above the water, I don't know what constitutes "high" light intensity. I'm sure some people have enough experience with both the AH Supply setups and the MH setups to be able to relate the two, but I haven't seen any widely accepted way to do so. And, maybe there isn't such a standard relationship. If you had AH Supply lights, and they were 4 inches or so above the water you would have 3.9 watts per gallon, which is a very high light intensity. With MH bulbs/reflectors located 19 inches above the water, I have no clue about how "high" the intensity is.

 

[mrkookm]

VaughnH,

Do you know how high Tom has those 1000MH mounted over that 1600g tank?

 

[VaughnH]

VaughnH,

Do you know how high Tom has those 1000MH mounted over that 1600g tank?

I don't, but I suspect reading the thread about that tank would tell us. But, tanks that big don't require as many watts per gallon, of any type, as the much smaller tanks we use. He uses MH lights on other, smaller tanks, though, so when he gets around to responding I'm sure he will have a recommendation.

 

[BHornsey]

It does seem a lot of light to me. I have a 6' x 2' x 2' tank and have three 70w MHs about 18" off the water and get good, steady growth.

I would say you could throttle back what you have and still get good growth. Raising them up some would also help. Try it and see

 

[mrkookm]

It does seem a lot of light to me

Yes I thought so too even though I had raised up to 19" so I raised the height to 21" off the water on Friday night after my initial post. I was pleasantly surprised to see all my plants reaching upward and not sideways when i got home yesterday, especially my Rotala Round which was growing like HM under good lighting! I have to start paying closer attention to what the plants are telling me, like they are telling me now that they like this height better

Halides are truly intense and I can't believe I had it at one point at 13" above water

 

[MacFanMr]

I have a pair of 400 mH's about 24" above a 215g tank. It was much more tolerable once I painted the wall behind it a dark matt blue color, but it's tons of light still. The plants were growing, but progress has come to a screeching halt now as the tank glass has developed multiple cracks. :-( Still... I think the setup is valid, you can check it out here: An Aquatic Obsession

 

[Tom Barr]

The 2x175w over a 90 is a lot of light.
You cannot maintain many species as they grow too fast to maintain their shapes and height.

70wx2 would be better.

Raising the lights up has a trade off.
You now are lighting the room
Or you need a huge hood.

I opted for another solution.
I still use lower light, but only 3-4" from the surface, this does not give spread throughout the tank though.

So to address that, I have made a a clock tracking device that slowly moves the light around a 40 gal cube in a 8" diameter circle(150w HQI).

I have a linear rail tracker planned for the 180 gal pair for the living room.
I'll get no light over spray, good use, good thicker foliage/growth, no hot spots, over lighted areas and the look will change throughout the day.

And I like gadgets and something cool unique on my tanks.

You can do something similar using a bank of 70w lights.