Who's eating my PO4?! - The Planted Tank Forum
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post #1 of 20 (permalink) Old 09-30-2018, 01:19 PM Thread Starter
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Who's eating my PO4?!

Hi

I'm having some odd issues with PO4 in my tank.
A little info, and background story:

I'm runing a high light, high CO2 tank with a lot of plants. I'm dosing daily with Tropica fertilizer(with NPK), and adding another brand for micro, as it seems too little micro is present in the Tropica.
Some time ago, I started getting some GSA, so I tested the water. Nitrates where fine, around 30~40 ppm right before waterchange, but PO4 was way low around 0,5 at most.
I hooked up some PO4 fertilizer to compensate.

It's been running for a week now, and it seems the GSA isn't going anywhere, seems to even spread faster on the not too old leaves. I did a new test and PO4 is still low.

What puzzles me is the amount of PO4 I'm dosing, just doesn't make sense compared to my tests of the tank water.
I'm dosing the easylife fosfo wich states 10mL per 500L tank is 0,1 ppm.
My tank i roughly 350L, so if I shoot for 2,0ppm PO4 the math should be like this:


10mL per 500L = 0,1 ppm.
10mL per 50L tank = 1,0 ppm.
70mL per 350L tank = 1,0 ppm
140mL per 350L tank= 2,0 ppm

The above example is my 350 L tank.

Now I'm currently dosing 50mL A DAY of the PO4 alone, on top of that I run the Tropica NPK ferts, and I often feed the inhabitants frozen foods which also has quite high traces of PO4.
I should have readings of around 5,0 ppm PO4 at the end of the week minus what the plants are using.

However I'm still getting readings around 0.5 ppm.
I've tested with to versions of testkits and an electronic tester with a +/- 0.1 ppm margin.

I'm really shocked seeing the PO4 getting used up like that, is this normal plant consuming this much PO4? Are my calculations way off?

What steps do I take now?
Add more PO4?
Empty the tank and look for a phosphate-eating creature in the gravel?
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post #2 of 20 (permalink) Old 09-30-2018, 01:41 PM
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Occasionally I have the same issue.
Have you tried just dosing the tank to desired level of 2ppm?
Then try to test for consumption just to have peace of mind.

Is mono-potassium phosphate available vs. buying all the water in a bottle?


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post #3 of 20 (permalink) Old 09-30-2018, 01:48 PM Thread Starter
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Originally Posted by Maryland Guppy View Post
Occasionally I have the same issue.
Have you tried just dosing the tank to desired level of 2ppm?
Then try to test for consumption just to have peace of mind.

Is mono-potassium phosphate available vs. buying all the water in a bottle?
Was actually thinking the same thing right now.
It's waterchange-day, so thinking afterwards dosing to desired levels, then keep en eye on it throughout the week.

Unfortunately, paying for lots of water and little ferts is the way to go here. I have however ordered the complete dry-dose kit from the UK, so hopefully it'll arrived soon. Tired of paying for water and I still have to add extra ferts anyway.

I'll do some math, and do the weekly maintenance and dose to PO4 to around 1.5 (I'd like to see for 1.5ppm PO4 after WC and 3.0 ppm at the end of the week.)
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post #4 of 20 (permalink) Old 09-30-2018, 02:06 PM
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Originally Posted by kilnakorr View Post
Unfortunately, paying for lots of water and little ferts is the way to go here. I have however ordered the complete dry-dose kit from the UK, so hopefully it'll arrived soon.
I checked your profile page before replying to determine location before I suggested compounds.
Almost think they should require a location be displayed for every member.
I've seen 10 replies before just to see the OP come back stating something is not available in their country.

Hope your dry-dose kit arrives soon!
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post #5 of 20 (permalink) Old 09-30-2018, 03:08 PM Thread Starter
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Originally Posted by Maryland Guppy View Post
I've seen 10 replies before just to see the OP come back stating something is not available in their country.
Very true - updated profile!

I hope I set the right dosing, but guess time will tell. Using those premixed fertilizers are a pain, and the amounts you need to dose are ridiculous.
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post #6 of 20 (permalink) Old 09-30-2018, 04:35 PM
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Sometimes tests are inaccurate. Try checking your test with a standardized amount of PO4 in some water to see if it reads correctly.
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post #7 of 20 (permalink) Old 09-30-2018, 05:38 PM Thread Starter
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Sometimes tests are inaccurate. Try checking your test with a standardized amount of PO4 in some water to see if it reads correctly.
Already have with the electronic tester and it's very accurate.

I little thing I just had to check up on:

I just did the weekly tank maintenance, and afterwards did a manual dose of PO4 but also micro ferts. Result is a little hazy tank. It seems PO4 and Fe precipitate.
Question is, since I dose everything with just a minute apart, could this be a reason for the low PO4 readings?
Could it be laying on the bottom of the tank instead of suspended in the water?
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post #8 of 20 (permalink) Old 09-30-2018, 06:12 PM
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A thought and suggestion which may only be to see if it is correct? Maybe test the fert being used to see what reading of phosphate? We know it should be simple fro the product to have the stated amount but then we do often find products which are NOT as stated. Maybe it merits some checking? Not sure how well that works out in a pre-mixed product but a thought----if it looks practical. Maybe a check to see how much the product changes water without the unknown of having plants and the monster to use any?
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post #9 of 20 (permalink) Old 09-30-2018, 07:46 PM Thread Starter
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Originally Posted by PlantedRich View Post
A thought and suggestion which may only be to see if it is correct? Maybe test the fert being used to see what reading of phosphate? We know it should be simple fro the product to have the stated amount but then we do often find products which are NOT as stated. Maybe it merits some checking? Not sure how well that works out in a pre-mixed product but a thought----if it looks practical. Maybe a check to see how much the product changes water without the unknown of having plants and the monster to use any?
Well, that is very good idea. I wonder why I haven't done this already!

Did the test and after my best calculations I was expecting a reading of 10 ppm.

Normal drop-test (hard to read at this concentration ) best guess 6-7ppm

Expensive electrical-laser test: 3.8 ppm

So, not really sure what to trust, but seems like the ferts contains less PO4 than stated.
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post #10 of 20 (permalink) Old 09-30-2018, 08:24 PM
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Quote:
Originally Posted by kilnakorr View Post
Already have with the electronic tester and it's very accurate.

I little thing I just had to check up on:

I just did the weekly tank maintenance, and afterwards did a manual dose of PO4 but also micro ferts. Result is a little hazy tank. It seems PO4 and Fe precipitate.
Question is, since I dose everything with just a minute apart, could this be a reason for the low PO4 readings?
Could it be laying on the bottom of the tank instead of suspended in the water?
I think this could definitely be your problem. Most people dose macros and micros on alternate days for this reason.

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post #11 of 20 (permalink) Old 09-30-2018, 08:33 PM Thread Starter
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Originally Posted by 64D-1701 View Post
I think this could definitely be your problem. Most people dose macros and micros on alternate days for this reason.
Unfortunately, my dosingpump can't be setup to dose on alternate days. I have changed the timing though, so micro goes in early and macros 5 hours later. Might make a difference.

At this point, I just hope my dry ferts arrive soon so I know exactly what I put in the tank.

I really don't trust these pre-made liquid ferts.
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post #12 of 20 (permalink) Old 09-30-2018, 08:45 PM
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Quote:
Originally Posted by kilnakorr View Post
Unfortunately, my dosingpump can't be setup to dose on alternate days. I have changed the timing though, so micro goes in early and macros 5 hours later. Might make a difference.

At this point, I just hope my dry ferts arrive soon so I know exactly what I put in the tank.

I really don't trust these pre-made liquid ferts.
Dry ferts are the way to go. I think your 5-hour separation will help. Definitely better than one minute.

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post #13 of 20 (permalink) Old 09-30-2018, 09:28 PM Thread Starter
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This really had me thinking and I looked for more info on the subject on Fe / PO4 reaction.
It seems quite clear this is an issue, but what's better than a simple visible test😁

So, I made a quick PO4 solution in two glasses and quickly added the smallest drop of my micro in one (for adding the Fe).

This really does have an impact on the drop-test.

Although the lighting isn't too good, the test with added Fe clearly shows less PO4 than the one with just PO4.
Hard to tell on the picture, but I can clearly see some stuff on the bottom of the Fe / PO4 mixture creating tiny bubbles.
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post #14 of 20 (permalink) Old 09-30-2018, 10:02 PM
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Isn't working with/against nature a wonderful thing?? We can think of 36 things to check and nature can throw out 37!
I'm thinking you are close to the answer. But maybe some thought on how to rearrange the dosing is worthwhile. simple life with automation just isn't simple, at times.
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post #15 of 20 (permalink) Old 09-30-2018, 10:54 PM
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For the dosing pump, can you have it dose macros say 9 hours before lights on and then micros 1 hour before lights on?

Phosphate is extremely active and will definitely interact with Fe. The problem is that Fe only lasts so long before the chelating/complexing agent breaks down and causes it to precipitate. This is why I prefer to dose Fe shortly before lights on if I can.

Having said that, I believe PPS Pro doses both on the same day, but the ppm dosed is a lot lower than EI which may reduce the impact. My bet is your 1 minute apart just wasn't enough time.
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