[APD] Re: how much light?

[Dgrim62 at cs_com]

This has been a very interesting thread to read, as I have been playing with 
light levels in my fairly new 240 gallon tank, which up until a week ago had 
four 175 watt metal halide lights about 12 inches above the water surface. My 
tank is 24 inches tall. I was having a very hard time with a couple different 
types of algae. I played with water flow and altered the amounts of 
supplements. I use CO2 injection with controller, and also dose nitrogen, potassium, and 
iron, in addition to maintaining GH with Equilibrium and KH with Alkaline 
Buffer. A lot of variables to try to see if any of these were helping or hurting 
the algae issue. 

Anyways, the tank is reef ready and has a sump of about 52 gallons capacity, 
which is usually halfway filled. So I'm thinking I have about 270 gallons in 
the water column. How wrong I was. I used this volume to get a rough idea of my 
light level, which came to 2.6 watts/gallon (700/270). Not bad, I thought.

Here are my errors (IMO): 

1. Just because a manufacturer says the tank is 240 gallons, it is not 
necessarily right on the money. The best way to get the actual gallons in your tank 
is to measure and multiply the tank's inside length x width x height in inches 
and divide by 231 cubic inches in a gallon of water. That will give you the 
actual gallons in your tank.

Some tanks are manygallons less than the label may say.

2. I stopped using the gallons in my sump to determine my light level. That 
amount of water never sees light anyways.

3. The amount of water in the substrate is minimal and shouldn't be 
considered in calculating watts per gallon, as this significantly inflated the volume I 
was thinking was in my tank.
 
So I redid my volume calculation measuring from the top of the substrate to 
the top of the actual water level in the tank, and multiplied this by the 
inside length and width, and got an actual net volume of 180 gallons, the actual 
amount of water moving around the tank at any one time.

This new figure 700 watts/180 gallons gave me 3.9 watts per gallon in my 
tank, big difference over the erroneous 2.6 I thought I had. 

I removed one of the Halides and now I have 525 watts/180 gallons or a real 
light level of 2.9 watts/gallon. The algae has slowed significantly and there 
is only a bit left now. I don't think this was the _only_ factor contributing 
to my algae problem, but when you are artificially accelerating the metabolism 
of your plants, I can only imagine that a very high light level can only make 
it harder to manage the other inputs (food-fish poop, CO2, ferts, N, K, Fe). 
Plant growth seems to have slowed down a bit, but the glosso is still hugging 
the bottom of the tank. I thought it might get taller. I set up the four 
halides following the rule of one 175 watter for every two feet of tank length. One 
175 watter for every 32 inches seems to be working well. 

My actual water column in about 206 gallons, as opposed to the 270 I thought 
I had. I'll use this figure if I need to dose meds or liquid fertilizer. I 
don't know how much actual water is in the substrate, but not much. I'd think 
it's role for dosing or meds as a part of total volume would be rather 
insignificant given the slow rate of turnover it is likely to have (just a guess).

Hope this helps.

Dave     


_______________________________________________
Aquatic-Plants mailing list
Aquatic-Plants at actwin_com
http://www.actwin.com/mailman/listinfo.cgi/aquatic-plants