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Phosphate in Tap Water: Hydroponic removal?


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#1 Guest_gerald_*

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Posted 01 December 2011 - 12:15 PM

This was prompted by Frogwhacker's 75 gal planted tank thread, but I figured it needed a new thread:

Like others have described, I too have frequent cyano slime blooms (Oscillatoria, I think) in new tanks or when doing large water changes on dirty old tanks. Usually they fizzle out eventually, but in a few tanks the slime is a long-term annoyance. I'm guessng the orthophosphate corrosion inhibitor in the city water supply is part of the problem.

SO -- Are there certain houseplants that are particularly good at hogging phosphate, that I could grow in a pot hanging over my water conditioning barrel, with its roots in the barrel? I refill the barrel after doing WC's, so the new water sits several days before going into fishtanks. I'm thinking an N-fixing plant would be best. My tap water is very soft (20-30 mg/l hardness) and has very little N.

#2 Guest_nativeplanter_*

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Posted 01 December 2011 - 12:33 PM

I don't know about N-fixing houseplants, but in general you will want to look for something in the bean family. Not sure which of these could be grown to maturity hydroponically, and if any need less than full sun lighting. Alfalfa maybe? Another problem you might have, though, is that since the plants would be grown hydroponically, they would probably need inoculating with N-fixing bacteria. Normally the bacteria are present in the soil (and one really does'nt need to buy inoculant for soil gardening, regardless of what the plant catalogs suggest).

#3 Guest_EricaWieser_*

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Posted 01 December 2011 - 03:34 PM

I did a quick pubmed search to see what people have tried as far as removing phosphate cheaply from water goes. Apparently it's popular to use something called 'biochar' which I guess is sort of like activated carbon. You take a plant, let it rot in a place without oxygen present, and then cook it really hot in a nitrogen-only (no oxygen) environment. I don't know about you but my oven lets O2 in and isn't so good at getting up to 600 degrees. And the housemates might object to the smell of rotting things in the apartment. So I kept reading, and then I found this article:

J Hazard Mater. 2009 Oct 30;170(2-3):511-9. Epub 2009 May 14.
Biosorption characteristics of phosphates from aqueous solution onto Phoenix dactylifera L. date palm fibers.
Riahi K, Thayer BB, Mammou AB, Ammar AB, Jaafoura MH.

They basically got some sheets of date palm trunk (Phoenix dactylifera), washed them in distilled water, and let them dry at about 220 degrees F for 24 hours. Then they put the fibers into the phosphate rich water and measured the absorption kinetics.

My oven can do 200 F, no problem, so that's totally feasible. And they reported that the equilibrium state (when all the phosphate that would absorb had absorbed) was reached within 120 minutes. That's cool with me; I waste two hours all the time. I have only one issue with this: Date palm fiber. I don't know where to buy it or how much it costs. The paper was published in Tunisia, where I guess there are lots of date palms. But here in North Carolina they are not so common, and the internet thought I was trying to buy a rug or something when I tried looking to buy date palm fiber online.

So if anyone can find some date palm fiber, let me know. I can totally see myself doing this to remove the phosphate from my water. Wash the date palm fiber, dry it at 200 F for a day, stick it in my filter for 2 hours and know that all the phosphate is removed. They report that they're able to get out 4.35 mg/g. That's awesome.

Edited by EricaWieser, 01 December 2011 - 03:38 PM.


#4 Guest_dmarkley_*

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Posted 01 December 2011 - 03:56 PM

This was prompted by Frogwhacker's 75 gal planted tank thread, but I figured it needed a new thread:

Like others have described, I too have frequent cyano slime blooms (Oscillatoria, I think) in new tanks or when doing large water changes on dirty old tanks. Usually they fizzle out eventually, but in a few tanks the slime is a long-term annoyance. I'm guessng the orthophosphate corrosion inhibitor in the city water supply is part of the problem.

SO -- Are there certain houseplants that are particularly good at hogging phosphate, that I could grow in a pot hanging over my water conditioning barrel, with its roots in the barrel? I refill the barrel after doing WC's, so the new water sits several days before going into fishtanks. I'm thinking an N-fixing plant would be best. My tap water is very soft (20-30 mg/l hardness) and has very little N.

Go to your LFS and get zeolites for removing phosphates. You can just put them inside your filter. They work great.

#5 Guest_EricaWieser_*

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Posted 01 December 2011 - 04:02 PM

Go to your LFS and get zeolites for removing phosphates. You can just put them inside your filter. They work great.

That sounds neat. How do you know when you need to replace them?

#6 Guest_Newt_*

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Posted 01 December 2011 - 04:58 PM

Azolla is N-fixing, thanks to symbiotic Anabaena colonies. Does your barrel have an open top?

#7 Guest_nativeplanter_*

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Posted 01 December 2011 - 05:07 PM

Azolla is N-fixing, thanks to symbiotic Anabaena colonies. Does your barrel have an open top?


That's right... I forgot about that one. And it's a fast grower, too!

#8 Guest_nkambae_*

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Posted 07 April 2012 - 04:15 AM

Any plant will uptake phosphorus. Nitrogen, phosphorus, and potassium are the big three in plant nutrients. They are the three numbers on the bag of lawn fertilizer... N, P, K. Non planted tanks can benefit from floating plants as they act like a nutrient sponge to soak up excess nutrients. However, cyanobacteria might not be the result of an overabundance of phosphorus. It can be (especially in a non planted tank) but it isn't always the case.

I add phosphorus to my planted tanks every week. The phosphorus I add is over and above what my local water works adds to our water supply. I am targeting 2-5 ppm of phosphorus in my tanks to keep my plants healthy which, I am guessing, is higher than that which your public works department is adding to your tap water. Call your local water department and request a detailed water report. I have found city employees to be eager to help out when they find a citizen who is actually interested in the details of their water quality.

Algae is very good at exploiting imbalances. Heathly plants in a balanced ecosystem seem to be able to outcompete algae but if there is an imbalance where one or more nutrients are limited and the higher order plants are no longer thriving, algae seems to gain a foothold and can easily overwhelm the other plants. A given watershed will not have the high levels of n, p, k I am striving for in my tanks but they are available in relatively unlimited quantities. So unless a feed lot overflows or there is a sudden increase in fertilizer run off form a golf course, farm, or housing develoment things stay pretty much in balance and algae is kept at bay. Some very eutrophic bodies of water have boom and bust cycles of green water and other types of algae and are similar in some ways to our glass boxes. Our aquariums tend to be very fertile and it doesn't take much to get them out of balance nutrient wise. Good luck.

stu

Edited by nkambae, 07 April 2012 - 04:18 AM.





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