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Thread: So here's the question.

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    So here's the question.

    Why is it so many people have no problem growing GHA in their tanks with all manner of nutrients, water quality, flow and just about any lighting conditions and yet......... They have problems growing it in a purpose made algae turf scrubber?

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    Time. The rocks have had month or years to accumulate growth.

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    Quote Originally Posted by SantaMonica View Post
    Time. The rocks have had month or years to accumulate growth.
    Well yes but that would suggest GHA would grow under lighting we would normally consider unsuitable for GHA growth. Often GHA arrives no sooner than the tank matures in some cases. In a scrubber light quality along with quantity and duration plays an important part in growing GHA. They don't seem to be as important in many people's tanks who's tanks can be overrun with GHA under just about any kind of reasonably bright lighting.

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    This is the argument that GHA grows in tanks under the high K spectrum, so why shouldn't one use a high K spectrum in a scrubber? Meaning, it would make sense to run all cool white and royal blue LEDs or 6500K+ light in your scrubber since that's what it's getting in the tank, and it's growing fine. Sound logic on the surface, but you have to consider intensity.

    In the tank, you have high intensity near the surface but lower intensity in the water. Also you have a spectrum loss with depth. The blues penetrate further, but the intensity is decreased. So you can get a lot of algae growth in the tank from the DT lights.

    But in a scrubber, you focus down to the spectrum that grows algae the best. If you put on blues and there is no depth of water to cause the same decrease in the intensity, you end up with too much light. That's not to say that you can't make a scrubber work with CW and RBs...it's just a much narrower window of operation.

    As you go lower and lower in the spectrum, you get much less intense light per watt and then you get into a range where you have a wider operation.

    I think most people that have problems with getting a scrubber going are missing something. Usually trying to over-light thinking more is better, or making it too big (same reasoning).

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    I go back many years in this hobby. When I started out we only had T8s or was it 12s? Anyway there was little choice just growlux and nothlight tubes. PAR was unheard of and certainly had it been measure it would have been extremely low yet many still had no problem growing GHA in fact it was the only algae many could grow. Sure nuitrents would be very high but light levels very low in tanks covered in GHA.

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    Right, I go back pretty far as well...30 years in FW to be exact. But you prove my point, you don't need much light to grow algae. What you need is the right light, and then you must provide an environment that is relatively better than than the DT for growing the algae.

    What matters is the now. Now, we have much more intense lights to meet the needs of certain corals. This means that you have to 1) get the algae to grow and have a foundation of growth upon which to build, and then 2) give it the superior environment. I think many skip past step 1 and try to blast a new screen with too much light and it never starts properly. Also growth on rocks which have nutrients available is different from growth on a bare screen or substrate. The latter will take longer to gain a foothold.

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    Quote Originally Posted by Bacon View Post
    Right, I go back pretty far as well...30 years in FW to be exact. But you prove my point, you don't need much light to grow algae. What you need is the right light, and then you must provide an environment that is relatively better than than the DT for growing the algae.

    What matters is the now. Now, we have much more intense lights to meet the needs of certain corals. This means that you have to 1) get the algae to grow and have a foundation of growth upon which to build, and then 2) give it the superior environment. I think many skip past step 1 and try to blast a new screen with too much light and it never starts properly. Also growth on rocks which have nutrients available is different from growth on a bare screen or substrate. The latter will take longer to gain a foothold.
    I'm not in disagreement with you just stating facts as I know them to be. Seems to me GHA will grow in almost all manner of light spectrum and intensity it's only the rate at which it will grow and or the type of algae that grows under various light spectrum which best suits it. I have seen GHA grow well under tubes mercury vapour and metal halides (HQI). We knew little of nutrients apart from nitrate but nothing of phosphate. Ammonia and nitrite was our concern in those days.

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    You do need red, and strong light, and air/water interface flow, and attachment, if you want to grow algae *fast*.

    Yes algae grows on rocks with white lights, but it's not growing fast. Remember that a scrubber (once growing well), can completely fill up in 5 days after a complete cleaning. The red simulates shallow water growth, which is where the greens mostly attach.

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    However to many its easier to grow GHA in their tank than in a scrubber that's my point. Seems the requirements to grow GHA in a scrubber are more demanding.

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    You're missing one factor and that is once your screen is established it can out-compete tank algae, if maintained right. I usually hear complaints of people scrubbing algae out of their tank (physically) and then it being back where it was in 2 weeks. But the amount that they harvest is not significant (squeezed weight) compared to what a good scrubber can grow in the same period, once it's matured. The key here is --> once the screen is mature <--

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