Phosphate control - The Planted Tank Forum
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post #1 of 18 (permalink) Old 12-09-2004, 04:27 PM Thread Starter
 
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Phosphate control

What is the best way to take phosphates out of water? Is there a special type of filter media, or does plain activated carbon do the trick? The reason I ask, is that I am having a slight algae problem. I am 90% sure the phosphate levels are causing it. I have a planted tank (not heavily planted), the plants have done a great job with the nitrates (5 ppm, currently) but the phosphate levels are still around 4 ppm. Is this high enough to cause the algae to out compete the plants? I have read that the trick to algae control is a balance of nutrients, am I just not balanced? I do weekly 20% water changes. I have cut back on feeding.

Part of the problem is the tap water. According to my tests, the tap water has levels of 1 ppm. I checked the test using distilled which read 0 ppm, as it should.

So what is the best way for me to remove the phosphates?

Algae killer is not an option, since it is not fixing the problem, just the symptoms.

Thanks
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post #2 of 18 (permalink) Old 12-09-2004, 04:48 PM
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That's a pretty high phosphate level you have there (relative to nitrates). You can run the tank at a higher nitrate level (10 ppm) and/or dilute the phosphate levels (1 ppm) by using the distilled water (check the KH and pH value of the water also).

Depending on how much water you're changing, you might consider a RO system. It might save you some money in the long run and you can use it personally yourself.

Eric


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post #3 of 18 (permalink) Old 12-09-2004, 04:51 PM Thread Starter
 
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What level should my phosphates be at?
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post #4 of 18 (permalink) Old 12-09-2004, 05:20 PM
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I had an occasion where the phosphate level got that high in my 40g tank (I guess I needed to do larger weekly water changes to get a better reset). I did several 40% water changes over a couple days until it got down to 2ppm.

What I noticed a couple of weeks ago was that my PO4 level was staying at ~2ppm even though my nitrate would get near 0. I ended up having to boost my potassium dosing. I guess, between my feeding and fish load I had a lot of NO3 and PO4 but was low on K. Now I add 2x the ppm of K that I do of NO3 when I dose. So if I add 5ppm of NO3 I add 10ppm of K. Seems to be working well as the PO4 level drops so that I need to add PO4 to maintain 1ppm

óBill

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post #5 of 18 (permalink) Old 12-09-2004, 05:26 PM
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You're shooting at 1/10 the amount of nitrates. So, if the nitrates are at 5 ppm, you're aiming for phosphate levels of 0.5 ppm.

In Bill's case, potassium is the bottleneck and ties down the uptake of both nitrates and phosphates (NPK are the macros).

I'm actually tracking levels of nitrates and phosphates as I battle over greenwater. At the same time, I've been monitoring potassium as well.

Eric


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post #6 of 18 (permalink) Old 12-09-2004, 05:30 PM Thread Starter
 
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1/10. Nice to have a rule of thumb to use.

So not having enough K will limit the amount of phosphates being used by the plants?
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post #7 of 18 (permalink) Old 12-09-2004, 05:41 PM
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Quote:
Originally Posted by fosteder
1/10. Nice to have a rule of thumb to use.

So not having enough K will limit the amount of phosphates being used by the plants?
Yeah. Basically, the plants will draw NO3, PO4 and K at varying rates until one runs out. Then the process gets stalled. The balance we strive for is to maintain enough of each in the system so that the stalling never occurs, but not so much that it causes an overload. For instance, an excess of K can sometimes inhibit the uptake of Ca. So what looks like a Ca deficiency is actually an excess of K.

óBill

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post #8 of 18 (permalink) Old 12-09-2004, 05:50 PM Thread Starter
 
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I take it this is something I will just need to get the feel for huh? If it is a short supply of K, is there any visual charachteristics I could check for? ie stunted growth, yellow leaves etc...
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post #9 of 18 (permalink) Old 12-09-2004, 05:56 PM
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Here's a useful link for you:

http://www.csd.net/~cgadd/aqua/art_plant_nutrient.htm

Eric


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post #10 of 18 (permalink) Old 12-09-2004, 06:06 PM Thread Starter
 
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cool! Thanks
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post #11 of 18 (permalink) Old 12-09-2004, 07:02 PM
 
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I've never dealt with phosphates in my tap water but 1 mg/l shouldn't be too bad.

Tom Barr has something like 1.2 coming out of his tap...

So maybe no need to get an RO unit just because of the 1mg/l level of phosphates.
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post #12 of 18 (permalink) Old 12-09-2004, 09:21 PM
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It isn't, as long as his nitrates are higher. At the present time, his phophate levels are almost as high as his nitrates....

Eric


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post #13 of 18 (permalink) Old 12-09-2004, 09:51 PM
 
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you might want to siphon off debris and junk off your gravel too. Get rid of teh source of phosphates coupled with 3X50% water change a week will drop it down in no time.
Thats how i got my algae control in my tank. After that reduce feedings and light. cut back on fertilizing. let it stabilize and then dose ferts again to find a balance.
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post #14 of 18 (permalink) Old 12-09-2004, 11:03 PM
 
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Good point Eric.
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post #15 of 18 (permalink) Old 12-10-2004, 04:34 PM
 
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make sure you don't overfeed...most foods will increase phosphate levels...something you don't want with 1ppm from teh tap.
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