Turf scrubbers vs. other nutrient export

[DWIZUM]

Thanks for the link. I'm a big fan of Randy but somehow missed that article.

Here's a silly question I haven't seen answered anywhere. What the scientific name for the specie(s) of algae that typically grow on these scrubbers?

[DWIZUM]

I think you said you haven't yet set up a scrubber but you have a reef tank you could try one with? Scrubbers are pretty simple and inexpensive to build, and what you learn might help in your planning for the 250g reef.

Sadly no - I've moved twice in the last year and have taken down all of my "serious" tanks, so I'll basically be building this 360g system as a first scrubbed system. That said, I tend to take things slowly and don't expect it to be fully stocked for two or three years, so I'll have plenty of time to experiment.

[jgreen1025]

Taking it slow is always wise regardless of the method used. As for the species of algae I think it depends on what's existing in your system. If you manage to grow true "turf" algae it might be a variety, but maybe it's a little more standard if it just grows the regular green hair algae. I found this quote by Eric Borneman (another reliable "Expert" in my opinion):

Eric Borneman Posted 5/14/2007
If you build it, they will come. If you want, you can scavenge little patches of various turfs from others, stores, etc. Inland Aquatics used to (and perhaps still does) seed their screens with a lot of species, and these went through successions. Mine currently remains dominated by Derbesia though I did seed some patches of a red astro-turf like species. It got outcompeted. Be careful, though. Some of the turfs that are on maricultured fragments, for example, are really invasive, and if you got those in the main tank, you might not be too happy. They are definitely not just intertidal hair algae. So, my advice is probably just let it happen.

My current screen has been running for just over a week now (prior screens have suffered from being unplugged by the cleaning lady and drying out, and a burned out pump... it's a long story) and it's got brown diatoms and a bit of green hair algae. Once it's working and the main tank is algae-free again I'll re-seed the sandbed - I use the mud and gunk from the bottom of the LFS live rock tanks (it's probably not a method many would dare to try, but it's always worked spectacularly for me). It will be interesting to see if that makes any difference in the algae that grows on the screen.

[DWIZUM]

Interesting. I'm asking about species because (especially given that article you posted) there's at least some information out there about how different species react to different conditions.

A question for those both successful and unsuccessful with scrubbers: Do you have any hard evidence to show what limits algae growth? Since we're using the algae as a tool to get unwanted nutrients out of the tank, I'd assume we would want to do whatever it takes to make sure it is those very nutrients that are limiting growth. Which means we'd want to play with lighting, flow, carbon sources, other nutrients that may not be available in the right proportions, etc.

[schnitm]

I recently added a second screen. Didn't exactly "need" it but I have a phosphate problem and while GFO is working very well...I can't help but tinker.

The second screen is identical in design to the first with one exception. Identical screen, identical lights (even replaced all the bulbs when I put it in), idetical plumbing, but... The first has about 35 GPH of flow per inch. The new screen has approximately 50 GPH per inch. This is a lot of flow and I'm having problems keeping it all attached.

The result after two weeks? The new screen is starving out the old one. The old screen is getting pale spots and was relatively thin at harvest on Sunday. I scraped more off the new screen (only two weeks old!) and it's a uniform forest green.

[kcress]

Nice test schnitm! So to repeat,, the higher flow is winning?

[DWIZUM]

The first has about 35 GPH of flow per inch. The new screen has approximately 50 GPH per inch. This is a lot of flow and I'm having problems keeping it all attached.

Did you actually get the flow totally attached though? Comparing these "sheet style" scrubbers to the old-school surge-style scrubbers, I'm wondering what role aeration plays in growth rates. In other words, is the faster flow important because it aids in aeration, or just because faster is somehow otherwise better?

[SantaMonica]

Can you explain your last "no?"

Algae growth is a function of light-power, i.e., wattage. You need the same wattage, CFL or LED, to grow properly. Using a low-wattage LED will grow nothing.

T5's are better because all parts of the bulb are near the screen.

Other than the mantra of "use spiral compact" is there any information available regarding the "best" intensity, spectrum, etc. of light for this turf algae to grow?

See the FAQ; that's was is currently known.

I've read plenty of success stories for scrubbers, but also plenty of "falure" stories. It's not always clear what separates the two, since often the techniques will seem similar.

It's clear to me. There has always been a glaring problem in the build/operation, that is, if they report it on my threads. If they don't, many times they can't figure it out.

I'm interested in knowing what typically limits algae growth in a system with a large scrubber and no other nutrient export. Are people seeing N and P sucked down to zero, or does one typically linger while the other is zero?

They both go down to unmeasureable values. Then growth slows. For us, it does not matter if it's N or P.

If you had the right light and flow, and N and P were both detectable in the tank, then I guess you'd have to look at defficiencies of some other nutrient.

No, then you have to look at an improperly built/operated scrubber.

how similar are marine turf algaes to typical FW plants in terms of nutrient needs?

I don't know. But I do know that FW and SW algae both fight for N and P.

Have there ever been efforts to supplement nutrients proven to be limiting growth in a scrubbed tank?

Minimal efforts. My opinion is that any limited scrubber growth is always due to build/operation. That's how every single situation works out.

Has anyone ever monitored O2 or CO2 levels in a scrubbed tank?

O2 is always high. But no monitored efforts as far as I know.

So, if not skimming, what forms of nutrient export did you compare it to in terms of export capability per watt consumed?

Everything else but skimming. Really, it's in the FAQ.

What the scientific name for the specie(s) of algae that typically grow on these scrubbers?

Don't know.

If you manage to grow true "turf" algae it might be a variety, but maybe it's a little more standard if it just grows the regular green hair algae.

Eric calls all scrubber algae "turf". But the type of turf that most folks are referring to requires a surge, and thus is not recommended as it is too difficult.

there's at least some information out there about how different species react to different conditions.

Yes but you have no control over what grows.

Do you have any hard evidence to show what limits algae growth?

Yes: Hundreds of scrubbers with clumps of algae that fell off into the system (from a non-rough screen). This truly is the limiting factor for most people.

We are a long way from needing to chemically tweak these systems; the biggest improvements are from just following the hardly-ever-followed guidelines.

The old screen is getting pale spots and was relatively thin at harvest on Sunday.

This is, as mentioned, probably clumps that fell off.

I scraped more off the new screen (only two weeks old!) and it's a uniform forest green.

Because it had a solid sheet of plastic to attach to, whereas the old one was spotted with dead roots which let go.

the higher flow is winning?

The more-attachable plastic is winning.

I'm wondering what role aeration plays in growth rates.

Nothing; air is not required.

[schnitm]

Hmmm...

Some algae is falling off the old screen but not much. 95% of what was there on the uncleaned side Sunday is still there. It's loosing it's color. Some almost looks white. I have not had attachment problems, although I think I have had the nutrient associated problems described in SM's last thesis.

The flow is different, but another variable may be the root of this. The "new" screen may have arrived at an opportunistic moment. This system had very high nutrient levels at the start followed by undetectable nitrates but high phosphates. Just before installing the new screen I droped the phosphates to undetectable with GFO. I am begining to suspect a species change is happening on the "old" screen. That screen developed in a high phosphate environment and the phosphates are now very low.

I'm going to leave things as they are and see what develops. Will also try to take pictures.

[DWIZUM]

SantaMonica,

Let me preface this post by stating that I'm not looking for an argument, or trying to disprove or cast doubt on your methods (which clearly work). Rather, I'm trying to understand the reasons why they work, so I can have the best chance at success. The way I do that is by asking questions. Hopefully that doesn't come across the wrong way.

Can you explain your last "no?"

Algae growth is a function of light-power, i.e., wattage. You need the same wattage, CFL or LED, to grow properly. Using a low-wattage LED will grow nothing.

I'm not sure about this assumption. A watt is a measure of electrical energy. A watt spent powering an LED does not produce the same results (in terms of light energy) as a watt spent powering fluorescent or metal halide. Photosynthetic organisms don't know or care how many watts are consumed by your lighting device, they care how much light energy you're producing. Hence, I would assume that if a particular LED fixture is producing X amount of PAR (or lumens, or lux - pick your favorite) in a certain spectrum, and a fluorescent fixture was producing the same color and amount of light, they'd have the same result in terms of growth on the scrubber.

However, you can certainly produce a certain amount of light energy more efficiently with LEDs, since they are capable of producing more light energy per unit of electricity consumed. I spend way more time than humanly reasonable thinking about and experimenting with lighting technologies over conventional reef tanks and planted FW tanks, so I know this is true in the general sense, even though I've never built a scrubber powered by LED. If someone has built a low-wattage HB LED scrubber and it has failed, I'd like to talk to them, to see what brand, model, bin, spectrum, etc. of LEDs they were using.

This is also why I'm interested in knowing the intensity and spectrum of lighting that works best on scrubbers. If 2700k CFLs seem to be the clear winners, then duplicating the same intensity and spectrum of light with LEDs should allow us to build scrubbers that are cheaper to operate in the long term (less electricity cost and no lamps to change every few months.)

[quote:ijmxrlbq]I've read plenty of success stories for scrubbers, but also plenty of "falure" stories. It's not always clear what separates the two, since often the techniques will seem similar.

It's clear to me. There has always been a glaring problem in the build/operation, that is, if they report it on my threads. If they don't, many times they can't figure it out.
[/quote:ijmxrlbq]

Again, I apologize for my lack of insight - I've read the FAQs and nearly every build thread on these and other forums, but I'm still failing to see a pattern. If you were to summarize into a few bullet points the most common modes of failure, what would they be?

[quote:ijmxrlbq]the higher flow is winning?

The more-attachable plastic is winning.[/quote:ijmxrlbq]

Does a certain flow rate play a role in success or failure?

[quote:ijmxrlbq]I'm wondering what role aeration plays in growth rates.

Nothing; air is not required.[/quote:ijmxrlbq][/quote]

Now I'm confused. I thought aeration was the whole reason these scrubbers were constructed the way they were (sheets suspended in mid air with a thin layer of water flowing over them, or the old surge-style where the sheet was exposed to air for several seconds/minutes at a time.) If aeration plays no role, why not just put the sheet underwater in a conventional sump and use a powerhead or natural flow through the sump to provide water movement?

Thanks again for taking the time to answer my questions.