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post #1 of 18 (permalink) Old 09-19-2011, 01:25 AM Thread Starter
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Question phosphorous/phosphate question

Greetings planted tankers. I recently got an API phosphate test kit to see if I needed to add a source of phosphorous to my fert regimen. First, does the test I got test phosphorous or phosphates or both? The test tells me I have 10 ppm of phosphorous without adding a supplement. Is this a lot, and how did it get into my tank? And finally, what do I need to maintain as a phosphate level in my tank for healthy plants? Thanks in advance for your help!

I even have duckweed in my water bong!
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post #2 of 18 (permalink) Old 09-19-2011, 01:35 AM
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I am no chemist but you can try to test your phosphate level on your tap water. See what shows up. That's one way phosphate can get into your tank. Another is from the fish food and fist waste. Another is from "chemicals" and "addictives" you added to your tank water. They may contain phosphate. Personally, I am not a big fan of testing unless my plants have "issues."
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post #3 of 18 (permalink) Old 09-19-2011, 01:36 AM
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I have never used API...but does sound like it would test the phosphates...you add phosphorus so...I believe they are one of the same......How old is the tank? How big? How many fish? Do you do water changes? How often do you feed?
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post #4 of 18 (permalink) Old 09-19-2011, 01:42 AM
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A phosphate test kit is worth very little if you don't calibrate it before using it. That means making some distilled water samples, to which you have added known ppm of phosphates. When you test those with your kit, you learn what the colors mean, how accurately you can judge the ppm from the colors, and whether the kit even works at all. A crude way to do this is outlined in one of the stickies.

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I have never used API...but does sound like it would test the phosphates...you add phosphorus so...I believe they are one of the same......How old is the tank? How big? How many fish? Do you do water changes? How often do you feed?
Tank is established (12+ month) 38g. Right now I only have ten glowlight tetras, two blue rams, two bronze corys and one dojo loach. Water changes once weekly, about 20% at a time. I feed this tank New Life Spectrum Small Fish food once per day. Since I added a bunch of plants, I have had a bit of difficulty cleaning my gravel- about two months ago was the last time I could actually get to the gravel with my vacuum but before then I did it twice monthly. I had a lot more fish in this tank but moved many of them to my other 38g when I decided to add plants.

I even have duckweed in my water bong!
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post #6 of 18 (permalink) Old 09-19-2011, 01:46 AM Thread Starter
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A phosphate test kit is worth very little if you don't calibrate it before using it. That means making some distilled water samples, to which you have added known ppm of phosphates. When you test those with your kit, you learn what the colors mean, how accurately you can judge the ppm from the colors, and whether the kit even works at all. A crude way to do this is outlined in one of the stickies.
Thanks Hoppy, I will take a look at the sticky and see if I can figure it out. Once the calibration process is complete, what is the target or ideal ppm of phosphates for a healthy tank?

I even have duckweed in my water bong!
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post #7 of 18 (permalink) Old 09-19-2011, 01:50 AM Thread Starter
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I am no chemist but you can try to test your phosphate level on your tap water. See what shows up. That's one way phosphate can get into your tank. Another is from the fish food and fist waste. Another is from "chemicals" and "addictives" you added to your tank water. They may contain phosphate. Personally, I am not a big fan of testing unless my plants have "issues."
Testing my tap water for phosphates is a great suggestion, thanks! I am normally not too concerned with water parameters unless I am tracking down a problem, but since I am new to planted tanks I thought it might not be a bad idea to learn what all of the associated parameters mean from the beginning. Thanks for your reply.

I even have duckweed in my water bong!
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post #8 of 18 (permalink) Old 09-19-2011, 02:59 AM
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Even after successful calibration, I found the results of the API phosphate test to be weird in a real tank, and additional phosphate was needed for good plant growth even though test levels were off the scale. More details in this thread:

https://www.plantedtank.net/forums/fe...fish-load.html
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post #9 of 18 (permalink) Old 09-19-2011, 04:07 AM Thread Starter
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Even after successful calibration, I found the results of the API phosphate test to be weird in a real tank, and additional phosphate was needed for good plant growth even though test levels were off the scale. More details in this thread:

https://www.plantedtank.net/forums/fe...fish-load.html
Thanks for the link and the real world info regarding the test itself. Are there any practical signs for getting an idea of whether or not I have sufficient/too much phosphate in the tank? Something like plant condition, or something else along those lines? If I had more experience with what to look for, I would probably not bother with the API test.

I even have duckweed in my water bong!
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post #10 of 18 (permalink) Old 09-19-2011, 04:11 AM
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Originally Posted by DarkCobra View Post
Even after successful calibration, I found the results of the API phosphate test to be weird in a real tank, and additional phosphate was needed for good plant growth even though test levels were off the scale. More details in this thread:

https://www.plantedtank.net/forums/fe...fish-load.html
This makes me wonder if all phosphates are bio-available, able to be used by the plants. I know some water companies add a phosphate compound to raise the pH of the water above 7, but I don't know if that phosphate is available to the plants or if it registers on that test kit.

I think you will also find that plants react very fast to phosphates when they have been deprived of enough. That makes it pretty easy to determine if you have enough. Just dose an eighth of a tsp of KH2PO4 per 40 gallons or so of tank water, and watch the plants to see if they perk up and grow faster, or even pearl. If you see no effect, do it again, and if you still don't see an effect you probably have some other problem, like inadequate available carbon. Also, inadequate phosphate often leads to green spot algae on the glass.

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post #11 of 18 (permalink) Old 09-19-2011, 12:54 PM
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Water companies might add a orthophosphate feed (basically a chain of phosphate I believe). It produces a PO4 residual in the water, which will cause a thin buildup on the insdies of piping to prvide protection against PO4. The plant operator general tests for PO4 at some remote point to make sure that it is in range. For us, we have a relitivly new system, with mostly PVC, and soft water, we keep PO4 at 1.4-1.6 ppm. Your water sytem might be different. In the town I lived in, it was higher.


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post #12 of 18 (permalink) Old 09-19-2011, 12:57 PM
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Oh, yah, I did get heavy green spot algae on glass at low PO4, but never really seen any negitive effects when it was higher.


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post #13 of 18 (permalink) Old 09-19-2011, 02:16 PM
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Water companies might add a orthophosphate feed (basically a chain of phosphate I believe).
Orthophosphate is more commonly known as phosphoric acid. Some reef tank folk say that algae has a particular love for phosphates in that specific form.

I would have to agree, because I have induced some crazy algae blooms using "pH Down", in the old days when it contained phosphoric acid. Later they put a warning on it not to use it in planted tanks because of that. And eventually they switched to sulfuric acid instead.

I have also seen people with high phosphate levels out of the tap, who have solved their algae problems by switching to RO water, or using a phosphate absorbing resin.

But you can add all the potassium phosphate fertilizer you want, and not cause algae.

My API test does register phosphate in my tapwater at about 1ppm. It's only for real in-tank readings that it goes nuts.

That amount is not enough to cause any noticeable algae problems for me. Nor has it allowed me to decrease my phosphate dosing. If algae can have a preference for phosphoric acid, then maybe plants have different preferences too; which would work out nicely for us.

I would love to see someone besides myself try replacing the potassium phosphate in EI with an equivalent amount of phosphoric acid and potassium sulfate, and report the results on both plants and algae.
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post #14 of 18 (permalink) Old 09-19-2011, 03:05 PM Thread Starter
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Thanks to all for your in-depth replies to my post. One of the things I really like about TPT is that when I post a question I will get technical information as well as practical advice. This really helps put a topic into context for me, and I really appreciate those of you here who share your hard earned experience so freely. I checked out my tap water, and it hits 3 ppm of phosphates, which makes sense considering I live in SW Florida. (Phosphate mining is big here in FL, and the presence of it in the aquifer explains the levels though there may be some added to the water as well.) The reading in my tank maxes out at 10 ppm, but I suspect it is higher than that; the test does not have a scale for any value above 10 ppm. I got some Flourish Phosphorous and will add this per Hoppy's advice to see if it improves my plants. If it does not, then at least I know that it cannot hurt. Some of my plants are doing really well (wisteria, Java Fern, Rotala, Argentine Sword) while some of them are not doing as well as I had hoped (Kompakt, Melon Sword, Amazon Sword) so I am trying to systematically track down what I may be lacking (or doing too much of) in my tank. At least now I am pretty sure it is not a phosphate deficiency. Thanks again to all of you who replied to my post.

I even have duckweed in my water bong!
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post #15 of 18 (permalink) Old 09-19-2011, 03:42 PM
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The swords are root feeders, and prefer to get their nutrients from the substrate rather than the water.

If your substrate is fairly inert, you might consider popping a root tab underneath each sword. I kept one in gravel and it did almost nothing for months, until I added a root tab, and it just exploded.
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