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Thread: New sizing guidelines

  1. #1
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    New sizing guidelines

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    What size scrubber do you need?
    (edited November 2022)


    Any scrubbing is good scrubbing. Even a small algae scrubber on a big tank will help your glass stay clearer longer. Beyond that, the basic guidelines for algae scrubbers are based on how much food you feed each day. These guidelines are to help you get the minimum size (or number) of scrubbers that will still do a good job of total filtration. You cannot "over scrub", so having a larger scrubber (or more of them) simply works more like the oceans and lakes do, which have enormous amounts of algae to do all the filtering. And the scrubber can go anywhere in your system; it will filter the same.

    So, scrubbers are sized according to feeding. Nutrients "in" (feeding) must equal nutrients "out" (scrubber growth), no matter how many gallons or liters you have. So...

    An example VERTICAL upflow or waterfall screen size is 3 X 4 inches = 12 square inches of screen (7.5 X 10 cm = 75 sq cm) with a total of 6 watts of red LED light for 18 hours a day. If all 6 watts of LED light are on one side, it is a 1-sided screen. If the watts are divided on each side of the screen, it is a 2-sided screen. This should be able to handle the following amounts of daily feeding:

    1 frozen cube per day (2-sided screen), or
    1/2 frozen cube per day (1-sided screen), or
    10 pinches of flake food per day (2-sided screen), or
    5 pinches of flake food per day (1-sided screen), or
    10 square inches (60 sq cm) of nori per day (2-sided screen), or
    5 square inches (30 sq cm) of nori per day (1-sided screen), or
    0.1 dry ounce (2.8 grams) of pellet food per day (2-sided screen), or
    0.05 dry ounce (1.4 grams) of pellet food per day (1-sided screen)

    Problem rocks: Each 50 pounds (2.2 kg) of nuisance algae covered live rock you have adds 1 cube a day. This rock is usually older than 3 years, or it's from another tank.

    Water flow or air bubbles is always 24 hours; water flow is at least 35 gph per inch of width of screen [60 lph per cm], EVEN IF one sided or horizontal.

    Floating surface scrubbers with strings: Screen size is the size of the box (Length X Width), and is 2-sided because the strings grow in 3D.

    Clean algae:

    Every 7 to 10 days, or
    When it's black, or
    When it fills up, or
    When algae lets go, or
    When nutrients start to rise

    However these are just starting points; a lot of your tank filtering (especially in saltwater) is based on your live rock, so their condition plays a part too in what size scrubber to make, as well as what type of feeding you are doing, and what other filters you will be using. Here are some specific guidelines:

    FRESHWATER:

    Since freshwater grows extremely thin, long algae, scrubbers without strings are recommended. This is because you will probably need to clean the scrubber in your sink with a toothbrush (instead of in-place harvesting while still in your aquarium), and it's easier to brush a flat wall than it is to brush strings. So flat-wall scrubbers such as wide-panel bubble upflows work well in freshwater. Also, since the thin stringy freshwater algae will flow out of holes in the scrubber, if you put the scrubber in your display (where the animals are), the animals will learn to eat out of the scrubber and you will therefore be able to feed less. If you intend to do a large part of your feeding this way, multiple scrubbers will allow the feeding (and filtering) to continue in one scrubber when you have cleaned the other. Waterfall types are not recommended for freshwater because the long thin growth flows down the drain.

    SALTWATER:

    With saltwater, you can get thick dense growth in the scrubber, which is when strings are an advantage (to hold on to the growth in the middle of big open compartments). So adding strings to a scrubber is acceptable, and the decision is based on size and on where you want to put it, and also on how you want to clean it. Saltwater tanks which use live rock (even if the rock is "dead") will need to take into consideration the history of the rock: If it came from a tank with algae problems, each 50 pounds (23 kg) of this rock will add 1 cube a day to your feeding. This is because the rock is really just coral skeletons which absorbed nutrients (mostly phosphate) from the water when the nutrients in the previous (or current) tank were high, and these nutrients will then start coming out and flowing into the water when your scrubber starts working.

    After looking at size, the main consideration is where to put it. Since scrubbers filter the same in any location, it is just a matter of placement. Unlike freshwater, the thicker growth in saltwater usually does not flow out of the holes or drains, so you can't rely on it for automatic feeding (although you can manually take some growth out). And similar to freshwater, multiple smaller units are better than a single larger unit.

    REEF:

    Reefs are the same considerations as saltwater, with the exception that some people like the reef to run as natural as possible, meaning it's filtered by algae alone. With that in mind, here are some more details and options:

    1) If you are building a reef tank which is new, and the rocks are coming from the ocean or from a low-nutrient tank with no algae problems, and if you will just be feeding the fish sparingly, and if you DO want to have other filters and water changes, then you can just use the cube-feeding recommended sizes of the scrubbers.

    2) If you are building a reef tank which is new as in #1 above, but you DON'T want any other filters or water changes, then double the recommended scrubbing amount in #1. This will supply the corals and small fish with the most amounts of food particles, and will allow filtering and feeding to continue in one scrubber after you cleaned the other.

    3) If you are building a reef tank which is new as in #1 or #2 above, but the rocks are coming from a nutrient-problem tank which had measurable phosphate or hair algae problems, then the rocks will be soaked with phosphate and this will supply more phosphate to your new tank than your feeding will. So use the guideline of 50 pounds of rock = 1 cube of feeding, to add to the recommend scrubbing size.

    4) If you are adding a scrubber to an existing reef tank, and the tank has no measurable phosphate and no nuisance algae, and if you have other filters and water changes and you DO want to keep them, then you can just use the cube-feeding sizes of the scrubbers.

    5) If you are adding a scrubber to an existing reef tank as in #4 above but you DON'T want to continue using the other filters or water changes, then double the scrubber amount recommend in #4, preferably by having multiple scrubbers which are cleaned alternately. This will keep one scrubber filtering and feeding when you have cleaned the other.

    6) If you are adding a scrubber to an existing reef tank that has measurable phosphate and green hair nuisance algae on the rocks, and you DO want to continue using other filters and water changes, then you can just use the recommended cube-feeding sizes. Use extra light (more LEDs) if possible because the higher phosphate in the water needs brighter LED's to make the scrubber grow green sooner. And if you double the amount of scrubbing (two units instead of one), the problems will clear up twice as fast because there will be twice the amount of algae absorbing the nutrients out of the water, especially when you clean one of them.

    7) If you are adding a scrubber to an existing reef tank that has measurable phosphate and green hair nuisance algae on the rocks as in #6 above, and you DON'T want to continue using other filters and water changes, then double the amount of scrubbing recommended in #6.

    8) If you are adding a scrubber to an existing reef tank that has NO measurable phosphate, but has LOTS of green hair nuisance algae on the rocks, then you need the strongest LEDs possible because the rocks are already full of phosphate, and the algae on the rocks is absorbing this phosphate, meaning you need the strongest scrubbing possible in order to out-compete the algae on the rocks. This is the hardest situation to fix, so you should use as much scrubbing as possible with the strongest LEDs available, and use as many other filters and water changes as possible too, until the algae on the rocks turns yellow and lets go. Be careful however, to start your scrubber with very reduced light, because very strong light will stop algae from being able to begin growing.

    End

    NOTE: The following posts, below, were from 2011 (the old guidelines), and are not about the current guideline above.

    NOTE2: This calculator might help, if it is still working:
    https://docs.zoho.com/sheet/publishe...b2b670ae00412b
    Last edited by SantaMonica; 05-12-2019 at 02:27 PM.

  2. #2

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    Re: New sizing guidelines

    Thanks, this is great info.

    Have just a little question when it comes to size / design of the screen:

    For example, have a screen that measures 10 cm x 20 cm the same filtering capability as a screen measuring 20cm x 10 cm?

    jnad

  3. #3
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    Re: New sizing guidelines

    Should be the same.

  4. #4

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    Re: New sizing guidelines

    So is there no more need to double the screen size if it's only lit from one side??

  5. #5

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    Re: New sizing guidelines

    Can only feed half as much for the same screen size if lit from one side.

  6. #6
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    Re: New sizing guidelines

    If all the watts are on one side, you can feed half as much, because the roots die faster.

  7. #7

    Re: New sizing guidelines

    i dont feed cubes. Usually a couple pinches of New Life Spectrum per day. Have a 130 gal FOWLR.

    was considering going with a 15 x 15 double screen with a 75watt bulb on either side. wat you think?

  8. #8
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    Re: New sizing guidelines

    No double screens.

    You probably mean a 13 watt bulb, which is way way too small for a 15" screen.

    See the feeding guideline at the top.

  9. #9

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    Re: New sizing guidelines

    Based on this guide, if I have a net of 90x20 cm = 1800 sq cm, that means I can handle 20x of food

    Is that correct?

  10. #10
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    Re: New sizing guidelines

    Yes, if you have 20x the watts.

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