Duckweed/HOB/Powerhead/Sponge-filter nightmare - The Planted Tank Forum
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post #1 of 5 (permalink) Old 06-30-2012, 03:59 PM Thread Starter
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Duckweed/HOB/Powerhead/Sponge-filter nightmare

As a preface, I've researched the absolute hell out of solutions for this, and just can't figure out where to go from here. Need some advice

So, one of the last times I went to the LFS, I was conned into taking home a large bagful of duckweed for my 55g. I'd always heard good things about it, in regard to helping regulate excess ferts and lowering nitrate levels. I had also heard the cons as in the inability to rid your tank of it, when you chose to do so.

I was running a Marineland Penguin 350 HOB filter on my 55. Hadn't even considered what this would do with the duckweed. Dropped in the duckweed and had a duckweed/confetti shower. Thought maybe it'd settle over time, that obviously didn't work. To solve this, I tried:

1. cutting out floating guards to go around the output splash from the HOB
2. tried raising the water level so that water just pushed out of the HOB
3. tried making a guard to corral the duckweed on the other side of the tank

These all worked temporarily, but never seemed to maintain. So after alot of reading and research on solutions for this, I switched to a Powerhead instead of my HOB. The powerhead I got had a prefilter attachment. This worked for about a day, then the next morning I awoke to the prefilter intake completely covered in duckweed and putting out nothing.

Started researching again.... found out I should try a sponge prefilter intake. I couldn't find one that would adapt to my powerhead, so I got some open cell foam from an Aquaclear sponge replacement. Cut it up into a good fitting rectangle around the prefilter intake. Worked great for about 3-4 days and was building some good bacteria on it, but this morning I checked the flow from the powerhead, and it wasn't putting out anything. I took off the intake prefilter, and the output increased, but I already think there has been damage done to the powerhead.

So my dilemma:

1. Take out all of the duckweed and depend on my 3 water sprites and 2 anacharis for absorbing excess nutrients, and be able to put the standard prefilter attachment back on (thus maintaining patent output flow and not burning up my powerhead)..... Or

2. Trying to find another solution whilst keeping the sponge prefilter intake from ruining my powerhead.

My main concerns are losing the duckweed's "buffering" capability by removing all of it (or atleast trying to)..... or on the flipside, removing the sponge prefilter intake and not really having a filter medium for keeping good bacteria growth. Has anyone else found a way to keep the sponge over the prefilter without burning up the powerhead?

Any thoughts would be great... and sorry for the extra long read
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post #2 of 5 (permalink) Old 06-30-2012, 04:06 PM
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women stockings at the end of your filter
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post #3 of 5 (permalink) Old 06-30-2012, 04:34 PM Thread Starter
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I'd heard that as well.

My biggest concern is just crashing my tank by either removing the sponge filter and all the accompanying bacteria..... and/or removing the duckweed and that extra purifying capacity.

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post #4 of 5 (permalink) Old 06-30-2012, 10:06 PM
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I have duckweed in most of my tanks, and sponges over the intakes of filters and some power heads.
When the water level is low the water returning from the filter (HOB, spray bar or other) will drive the duckweed under water, and it sure will get sucked up against the sponges of any sort of pump (power head or filter).
I find this to be a temporary problem, though. When the water level is higher the filter return sheets across the top of the water, and pushes the duckweed away from that area of the tank without driving it under water.

Yes, sponges over the intakes of filters and power heads will accumulate debris and will need cleaning. Every few days seems like a lot of cleaning, though. Mine usually go a couple of weeks before slowing down, and another week before it gets to the point that I am worried about the flow. You could try a coarser sponge, for example there are sponges sold for sumps or ponds that are coarser than the Aquaclear sponges. I use a lot of Aquaclear sponges, but if the sponges in a particular tank seem to need cleaning too often I will switch to the coarser sponges. Coarser sponges let the finer debris through for the real filter to trap. I have found that if I use the Aquaclear sponges over an Aquaclear filter the sponge inside the filter (same cell size as the sponge over the intake) no longer does its job. The sponge over the intake is trapping the same debris that the actual filter sponge would have.

Sponges with a larger surface area are a good idea, too. There are 2 main ways to do this. One is to use a Mattenfilter sort of set up. There is a long thread in the Low Tech forum about this. The other is to make a manifold out of PVC with several Ts, and put a sponge over each T. That is the way I do it. Instead of one sponge, and moving 100-300 gph though it, I have 3-5 sponges per filter and each sponge draws less than 100 gph. This also makes the force of the water less at each sponge, so even weaker fish can swim near the sponge or graze on it and be able to get away.

Removing all the duckweed just takes patience. Net out all you can daily and set up a power head that makes a distinct current at the top of the tank. This will push the remaining duckweed to one end of the tank. Remove equipment from that area and keep on scooping out the duckweed. It will take time, but a clear area to scoop it from will really help. By removing it slowly, over a couple of weeks, you are encouraging other resources to take over the nitrogen removal. You could also get some more plants such as Anacharis or Water Wisteria that are noted nitrogen sinks, and easier to handle than duckweed.
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post #5 of 5 (permalink) Old 07-01-2012, 01:22 AM Thread Starter
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Thanks for your reply Diana!

I've def looked at the Mattenfilter designs and considered those.

I actually lowered down my powerhead farther into the tank today, and aimed up the output a bit steeper. It's still maintaining good surface movement, but not so close to the duckweed getting sucked under. From doing this, I was able to just put back on the little pre filter mesh screen and remove the sponge. I'm letting the sponge ride the current around in the tank though, to maybe help distribute some of the bacteria to the walls of the tank.

I think I've just decided to move away from the duckweed. I do have an anacharis in the tank, and several water sprites (which I've always read are good for absorbing excess nutrients and nitrogen). If that doesn't seem to do the job, I can look into some larger floater plants.

Did a 50% water change last night as well, and this morning had a surge of new green growth

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duckweed, powerhead, prefilter, sponge

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