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That's great, Hoppy. I'm watching this with interest. You and I have something in common - we both share a love for running scientific experiments. Having a background in the physical sciences, I need to get my 'fix'.

Am I right in thinking that you have done a good many measurements on aquarium lighting? Your name is carved in my memory banks from a few years ago.

Yorkie
 

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Yes, you are remembering right. I spend several years trying to find ways to determine how much light we have and how much we should have. It is still a mostly a guesswork subject.

When I got back to this hobby about 25 years ago, after I retired, I did it largely because there was so much to learn, and so much that was unknown about the hobby. I have never regretted that decision.
Hi Hoppy,

Thanks for your reply.

I also have a particular interest in aquarium lighting. There seem to be very few lighting manufacturers who design their products with the needs of plants in mind. And they blast aquarists' tanks with loads of photons at wavelengths that plants cannot use but algae and cyanobacteria bask in this light. But, I do realize that we want our plants to look right - not a weird shade of pink! This is not horticultural lighting.

JPC
 

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I think the biggest lack of information we now have is algae and why it grows or doesn't grow. Diana Walstad's book is, in my opinion, on the right track in saying that it is the nutrients in the water that are the key to having algae or not having it. Algae have no access to the nutrients in the substrate, except for what leaches out into the water. And, I'm intrigued by the idea that it could be iron in the water that is the magic key to algae problems. Unfortunately, it is also very hard to find a good experiment that could enforce that idea.
Hi Hoppy,

Diana Walstad, in her book, talks about light wavelengths below 520 nm promoting algae growth. But, plants also need light from this part of the spectrum. Chlorophyll a and b peak responses occur at 430 nm and 453 nm, respectively. However, with a lighting fixture that permits control over its spectrum, the amount of light being emitted below 520 nm can be reduced. The fact that white LEDs are essentially blue LEDs with the appropriate phosphor added results in a lot of light from 400 nm - 520 nm, as I'm sure you are aware. Please see the attached.

Yorkie
 

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Yes, I have seen those charts, but I haven't seen any data that would support a belief that certain wavelengths of light cause algae problems. That, too, is a very hard experiment to try.
Hi Hoppy,

Perhaps I've confused things by referring to the chlorophyll a and b peaks. I wasn't suggesting that specific wavelengths could promote growth of algae. Diana Walstad has drawn that to our attention by introducing us to iron photoreduction at less than 520nm.

Now, I do want to suggest that certain wavelengths may indeed promote algae (and BGA). Please see the attached absorption spectra. The two accessory pigments, phycoerythrin and phycocyanin are to be found in BBA and BGA, respectively. So, light in the band from 500nm to 620nm may have the potential to promote both BBA and BGA. And, higher plants only require a small proportion of light in this band. I may have suggested elsewhere on this forum that reducing the intensity of light in this mid-band when the tank is not 'on display' may help to reduce BBA and BGA. Then, when the tank is 'on display' for the benefit of we humans, the spectrum would switch to one that is aesthetically pleasing.

Yorkie
 

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My experiment isn't going to be a success. I suspect I don't have enough substrate in it, and the plants are not doing very well as a result. But, if I can't get both sides of the tank to start out doing well it isn't possible to see the effect of changing something on just one side. When I think about this some more I will probably start over again, but I need to keep the two betta's living while I do it. I'm still intrigued by what I read in Diana's book about iron.
Hi hoppycalif,

It's a shame that the plants are not growing well and that your experiment will not be a success. I will follow this with interest should you decide to try again.

Yorkie
 
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