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If I use a 20w bulb over a 12 inch deep 10 gallon tank, I am supposedly getting 2 watts per gallon.

If I use a 20w bulb over a 12 inch deep 20 long tank, am I still getting 2 watts per gallon, so to speak.

I've just added co2 and am seeing good results even tho the co2 levels are not the highest. The pH is holding at 7.2 and the kH at 4.48 dkH, despite going from 1 bubble ever 3 seconds to 1 bubble every 5 seconds on the nutrafin.

I've got a double strip light I can use, but last time I put it on my tank, my fish all went beserk as it was so bright on such a shallow tank. Even I thought it was too bright to look at with 40w.

Looking at the 20 gallon tanks, there is a 20 regular, a 20 tall and a 20 long. If I put a 20w bulb on all of these, the light intensity at the bottom of the tank will differ for all of them, so is the watt per gallon really a good measure? The way I see it, I'm getting about 1.5 watts per gallon, at least.

I managed to grow cabomba for a good while under that light before co2. I've since added it back in, along with more hornwort and have placed it in the brightest part of my tank. Other than that, I've got some slow growers.

Banana Plants x3
Anubias Nana x2
Java Fern 1, plus 3 babies
Val Spiralis x1 (new growth seen since adding co2)
Najas Guadalupara x2
Java Moss

I really don't want to add more light, unless the plants demand it. I know the plants would grow faster with it, but the last time I used 40w, the tank was nervous for the entire 2 months it was on there. The fish stayed under some plant or another all day long, just not interacting the way they do under just 20w.

Oh - and I used Lime-Off on the glass canopy to get it crystal clear and free of the lime deposits obstructing the light. IT is much bright now than ever.


Last edited by Cory_Di at 02-Mar-2005 11:02

Last edited by Cory_Di at 02-Mar-2005 13:31

You bring up a good point about the WPG rule.

It's just like the "inch of fish per gal" one. It is more of a guide.

I see no reason why a plant that is rated at a higher output WPG can't be kept in tank with less WPG, as long as the light source over it meets the needs of the plant.

I would not advise a person who is new to plants to try this, and I think that is why they just standardized the rule.

But hey, they are only plants...If it doesn't work out, your only out a couple of bucks, instead of a life (fish).

Now for the part about your fish not liking the extra light.

You will find that if it bothers them, they should be better once the tank has grown in and the light is blocked by the plants. Kinda like a tree canopy in the rain forest, just not as extreme.


Last edited by Shannen at 02-Mar-2005 11:29

Have you thought about adding a reflector instead of doubling your light? It does make things brighter, but not as bright as doubling the light output.

I suppose I could try that, but how do you do it?

You can buy them from a lighting shop. It fits between the bulb and the canopy.

Most modern hoods already have some form of reflector in them tho. Least here in the states they do. You should check yours.

You can even make your own outa tinfoil..It's not as good but it should do the trick.

shannen is correct about the wpg. it's all about intensity at certain depths, and if you had a submersible light meter, you would probably find that you are getting the same intensity at the bottom of the 10g and 20g, even though one is "double" the size of the other. and also, depending on what kinds of plants you have, eventually you *will* block out parts of the light once they grow up (and out).

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"That's the trouble with political jokes in this country... they get elected!" -- Dave Lippman

That is pretty much what I have thought, yet so many times people have mentioned that I need to up my lighting.

it also depends on what plants you have. some plants require much more lighting than the average light strip, so if you were to get one of these higher maintenance plants you would have to eventually get a higher wattage for your tank.

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"That's the trouble with political jokes in this country... they get elected!" -- Dave Lippman

What about the plants I have in my list above?

well, except for the banana plant, your other plants don't have very demanding light requirements. if the banana plant is growing well, then your other plants should be thriving. if you notice your bananas having any problems growing then you should think about upgrading your lighting, imo.

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"That's the trouble with political jokes in this country... they get elected!" -- Dave Lippman

Banana plants having a problem? Not!

One of my 3 banana's took off so fast BEFORE I added co2. Within a week of planting it, I was graced with several 5 inch diameter leaves, followed by a trio of lily pads that I allowed to grow, just to see what would happen. I cut them after a couple weeks. A few of the bananas went soft after that and I just pinched them off, but it continues to produce new leaves. The other two banana plants aren't as robust, but are nonetheless growing slowly.

My Val could probably use more light, but its all by itself on one end of the tank - next to the co2 source, conveniently.

Since adding the co2, those banana plants are looking a much deeper green than I've seen before. I kept dosing fertilizers, then figured they were suppose to be lighter green. It is a very healthy green.

It's only been about 30 hours since I added the cabomba and let me tell you it has twisted and turned right up to the center where the light is strongest. Go cabomba! I love the look of that stuff.

Last edited by Cory_Di at 02-Mar-2005 18:47