How much does size really matter?

[druckle]

As I understand it from reviewing many posts it is recommended that an algae scrubbers size should not be bigger than a certain number of square inches based on the amount of food entering the water column.

I am having a hard time understanding this. I can understand that there would be a minimum size requirement based on the total nutrient load present but why a maximum size?

My thinking goes along these lines. An individual alga cell needs sufficient light and nutrients as well as sufficient water flow to deliver and remove gases to achieve its maximum growth. Each individual cell will thrive if the conditions around it are satisfactory. That individual cell is not a thinking individual though. It is not aware whether a cell located far from it is surrounded by the same conditions that it is so it's growth will be determined by its own conditions. Now say that we reduce the nutrients only (leaving light, water flow etc. the same). This is the desirable condition for the aquarist right? If the nutrients delivered to it are not optimum for its growth it will grow slower or another type of alga cell with different nutrient requirements will begin to grow. This, now environmentally favored, algae may be something other than the green algae preferred by the aquarist but it will still be an alga cell that grows (uses nutrients from the water etc.). This is what happens in the ocean or even in our aquariums. At one location one type of algae may grow but at another location another type of algae may grow based on the local environment.

From this it seems to me that the limit on the area of the screen is really saying we need to decide on a level of nutrients that should be left behind in the water column and size our screens to be sure that there is sufficient contamination of the water column to maintain that level of nutrients available for the favored green algae growth. Is that really the essence of the recommendation to limit a screens size? If so, shouldn't we be measuring the total chemistry of the water column and basing our screen size recommendations on that? I understand that such measurement may be difficult.

Is it really known that the animals in our aquariums prefer the level of environmental contamination left behind by green algae growth and detest the environment left behind by black, brown or yellow algae?

Now if my screen is too large (per the recommendations) but all the controllable parameters are in the "right" range I can understand that the growth rate of the algae on the screen will be changed, or the type of algae grown may be different based on the lowered nutrients available but is this so bad? If only the growth rate is reduced that means that maybe I won't have to clean the screen as often and I will still maintain relatively healthy algal cells. If the type of algae changes, what would happen at certain location in the ocean. Is it really known that the animals in our aquariums prefer the level of environmental contamination left behind by green algae growth and detest the environment left behind by black, brown or yellow algae?

If the living animals in my aquarium are responding well to the low level of nutrients and whatever type of algae is growing, should I really be worried about the color of the algae on the screen?

OK...there is this other factor of removing too many nutrients from the water column for some species of coral to be in their optimum environment. I can understand that, but one way to achieve that would be to slow the growth rate of the algae by reducing it's time of exposure to it's optimum light levels. I think I have seen this mentioned many times as a recommendation to achieve the favored green algae growth under certain conditions.

I know we can never really recreate the conditions of the ocean. Even the ocean conditions vary greatly throughout that massive water column covering much of the earth but we are trying to create our own little ocean with conditions that allow us to keep our selected animals and plants in a condition that pleases us so.........

My real question is what bad thing is going to happen to my aquarium's inhabitants if my screen errs on the side of "too big". Are my animals all going to suddenly die? Will they become sick and look lousy?

I'm sorry if this has all been covered in detail. I have tried to read through many threads but I haven't found information that's seeped in my brain to take away my basic question. Why is "too big" really a bad thing?

If it is not really a bad thing to have a screen that is too big for my aquarium as it is today, then a screen larger than the currently recommended screen might just allow me to increase the feeding load I supply to my aquarium without having to tear down my scrubber and rebuild it each time I acquire more animals or increase the rate of feeding of the current animals. At least that is my thought. If "too big" is really bad then how often should I be rebuilding my scrubber as I increase my feeding load?

I hope I'm not beating a dead horse here. I know some of my thoughts may be rambling but this is the stuff that's going through my mind as I contemplate getting serious about building an algae scrubber.

[Floyd R Turbo]

druckle, welcome to the site. Lots of good questions. Let me see if I can help answer them.

Screen size: You can make the screen bigger and that probably won't harm anything, but I would recommend not exceeding a size that is 2x the largest amount that you plan to feed. Then go with an array of LED lighting made from good quality 3W LEDs, one on each side for every 4-6 sq in of material. This will be a "high light" screen, so you would only need about 9 hours/day, then if you had a drastic increase in feeding/nutrient, you have room to increase the light photoperiod without having to adjust the screen size. You can also reduce the photoperiod or maybe even put 1/2 the LEDs on one driver and only run half of the LEDs if you wanted to, that would be anothe way of tweaking things to your liking.

The dark algae blocks light to the lower layers, which means the 'roots' beneath that will get less light, and they will start to die off which releases nutrients back into the water. So yes, dark algae is bad. yellow rubbery algae also blocks light very well and the same thing happens. GHA is stranded and moves back and forth in the flow, which allows light to penetrate better. It is largely because of this that GHA filters best and is desired. There are other factors as well but this IMO is the main one

If you have a screen that is too large, the growth can tend to spread out and less nutrients are available per unit area (for lack of a better way to explain it) so you will get likely a similar amount of green growth but more likely a higher percentage of light-blocking yellow growth, meaning that your hope to not have to clean as often is offset by the fact that you are growing more light-blocking growth. I hope that makes sense.

But what you really want is very intense lighting and high flow so that when filtration (photosynthesis) is occurring, you are getting the best type of growth. Dialing back the intensity and prolonging the photoperiod will promote the wrong growth, so you don't want to do that. Make the scrubber very strong, and shorten the photoperiod. EDIT: Now that I wrote that I notice that it sort of conflicts with the 1st paragraph I wrote, where I mention making the array 1/2 and 1/2 on separate drivers. But LEDs generally give you the intensity you need, and you can go with fewer LEDs and be OK whereas fewer watts of CFL will cause a large drop in intensity that will cause you problems.

As for recreating the ocean conditions, one could argue that the algae scrubber is no where near ocean conditions. In fact there is a good argument for that. The fact is that we are taking a mechanism that exists in the ocean and amplifying it to utilize it's best features to the maximum amount possible. While the algae itself is natural, the algae scrubber is rather unnatural. Just like wave-action produced foam on the beach is natural, but foam fractionation is not natural. Just like bacterial filtration is natural, but carbon dosing is not natural. These are all natural mechanisms implemented in non-natural ways in order to maximize their performance in a small, simulated environment that itself is inherently unnatural. So there's nothing bad I'm saying here, but I just cringe when someone refers to anything in this industry as natural. Sorry, I'm off my soapbox. I think we're on the same page...we're all trying to simulate things!

But no, your creatures are not likely to suddenly die because of a scrubber being too large. It just might not filter to the best ability as it was intended. For years, people ran scrubbers (myself included) that were vastly oversized per the feeding guidelines and most of the time, they worked just fine. The smaller sizing guideline just makes more sense as it is nutrient related vs volume related, and it also makes it a lot easier to build one for many different sized systems, and in cramped sump areas (which most of us have).

[druckle]

Thanks for your thoughts on scrubber size FRT. I really appreciate it.

I'm one of those guys who loves to have the most absolute understanding I can achieve so I've decided it would be good to put some numbers to as much of my scrubber understanding as possible. I'm putting together an upflow experiment which will allow me to change the number of LED's for various frequencies, the intensity of each, the size of the array, the size of the screens, water and air flow rate over the screens including the angle of incidence of impinging flows and angle of the screen. I'll be controlling the level of contamination of the water by starting out with fresh seawater and dosing it to the same starting level of nitrates, phosphate iron etc. for each segment of the series of experiments. Sounds crazy huh? I figure if I document the change in water quality and the resulting algae growth with time I will learn something and if it confuses me when I'm done then at least I'll know that there are some things that I just will never really know and that's how it is.

This is all going to take some time but with multiple scrubbers going at one time I may have some real data in this lifetime. I'll try to let folks know what is happening real time as it happens. I hope it will be useful.

[SantaMonica]

Welcome.

The thing you did not account for is growth thickness. If the screen is bigger, there are not enough nutrients to grow it thicker. So you never get gha. And gha is what reaches out into the flow and lights the best, and thus filters the best.

[Floyd R Turbo]

Ah yes, I knew I was missing the way to describe that concept. Condensing the screen area to force the growth to occur in a smaller area also forces the algae to grow outward instead of sideways (spreading out over larger area), giving preference to GHA which does this the best. I woudn't say that you would never get GHA, but it wouldn't necessarily be the preferential type of algae growth, depending on other factors (flow, feeding, light, etc). And you want it to be the preferential algae.

[druckle]

Thanks for the suggestion to monitor thickness guys. I hadn't really thought of that as a critical parameter. I was almost entirely focused on water quality achieved and maintained over time. I'll add that to my list of things to document.

[druckle]

Just a quick thought... Isn't hair still algae still hair algae even though it's short? Not intending to be argumentative (I'm curious, not arguing) but if the algae that grows on a big plate is the same species as that on a smaller plate isn't it still doing the same job one way or the other? I can't see why forcing it to grow long is better than letting it expand over a larger surface albiet at a shorter length. If the conditions are right for that species of cell won't it grow favorably compared to other algae species.
I will determine the thickness parameter while I'm monitoring everything I can about water quality. I think it's an important thing to know.

I do see btw how it is more efficient to have the smaller plate. Takes less space, costs less money to build etc. I still have to find the numbers that say that I'll get better and more consistent water quality with a smaller plate. Stubborn old turkey huh?

[SantaMonica]

Longer will reach out more into the flow and light.

[druckle]

Yes Santa Monica. I agree. But longer will also restrict the light near the screen possibly causing alga cell death and decomposition in that area sooner than with a thin layer of algal cells over a larger screen right?

Does anyone have numbers on the resulting water quality and stability with small vs. large screens with the same flow, lighting frequency and par values? I really don't want to do this whole experimental thing if there are numbers confirming the differences in scrubber behavior.

[Floyd R Turbo]

Not from a purely scientific experimental basis, no. I have plans in the works to start a few growth-related experiments so I can 'test' growth rates with various configurations. But first, the baseline is needed. That is, the control experiment which can repeatedly grow a consistent quantity of algae under a given set of circumstances.