# Re: [APD] Re: how much light?

```--- Dgrim62 at cs_com wrote:
> 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. >
> Here are my errors (IMO):

A 240g! Now that's a tank with some elbow room for jungle
farmers like me, who is stuck with a measly 150g tank
(nominal size).

>
> 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.

Being fond of rules of thumb, because they are easy to
remember, easy to pass on, and generally practical, I
measured a few tanks, adjusted for substrate -- never
counted sump water but just the size of the space being lit
-- and decided that a reasonably good figure to use is 80%
of the manufacturer's stated nominal size for the aquarium.
(Has anyone found a tank whose internal volume was larger
than the nominal size?) Yes, there's lots of variance and
wpg is only a rule of thumb itself since bulbs, reflectors,
ballasts vary.

So is a wpg rule of thumb based on nominal or actual
volume? I guess you'd have to ask each person that states a
wpg rule. One could express a rule either way.  When I do
it, I have in mind the nominal size because it's one less
thing for folks to have to measure and compute. But even
the 20% adjustment, wouldn't get my rates quite down to
George's levels.

Of course, I never said anyone *should* have a high light
level of 3-4 wpg. Or that someone should have a high light
or low light or fast grow or slow grow aquarium. I have
diff kinds and find them all intersting, each in somewhat
diff ways. But I think there's a diff between my view and
George's. He seems to think more than 2.5 is inappropriate"
whereas I think it's high, doable, harder to maintain a
tank at that level but lots of folks seem to do it.

Scott H.

=====
S. Hieber

__________________________________
Do you Yahoo!?
Free Pop-Up Blocker - Get it now
http://companion.yahoo.com/
_______________________________________________
Aquatic-Plants mailing list
Aquatic-Plants at actwin_com
http://www.actwin.com/mailman/listinfo.cgi/aquatic-plants
```