Can anyone help calculate the error I have made with Phosphate?

surcalation · Oct 22, 2019

Basically I need to work out how much phosphates I have actually added to my tank in a very naive way.

Have had 0.0ppm phosphates on my Hanna Checker for 6 weeks and Nitrates have crept down to 1.0ppm started to see signs of dinoflagellate and had tried for a couple of weeks doing all the things you would tell some with high phosphates not to do. I read that food grade Potassium dihydrogen phosphate would be a good way to get some phosphate in the tank and boy did I.

I took 4 litres of salt water and added 4g of Potassium dihydrogen phosphate to it. I then measured this with my Hanna checker and I got a reading of 2.4ppm. so I thought ok, 2.4ppm divided by 4 gives me 0.6ppm per gram of Potassium dihydrogen phosphate.

10g of potassium dihydrogen phosphate into 1000l water would give me a reading of 0.006ppm so would probably take me 10 days to get to 0.06 as the desirable region. So I decided I wouldn't test until day 3 so that it would be detectable.

THAT IS WHERE IT HAS GONE HORRIBLY WRONG. Tested with my Hanna on day 3 and it just flashed 2.50ppm at me. I thought maybe just an error and testing again. Nope exactly the same. Realisation that the maths is wrong started to dawn on me. I have put X3 mixes of 10g Potassium dihydrogen phosphate with 500ml water in the tank.

I have picked up a Salifert test kit for Phosphate its way cheaper than trying to get a number on my Hanna. I also have started dosing Quantum Phosphate remover (lanthanum chloride) at 50ml for 1000 litre which is supposedly for tanks with 5.0ppm to 10ppm. Have done three doses so far and still at 3+ppm on the Salifert.

Can anyone calculate how much I messed up by in ppm so I can sort it? Have got my rowaphos reactor online too. Refugium lighting extended etc.

Bayareareefer18 · Oct 22, 2019

Are you using a 10 micron sock with the LC to remove the precipitate?

surcalation · Oct 22, 2019

No as I run the Triton method so don't run filter socks. My protein skimmer is running though but on the dry side. Rather than a wet skim.

Is me not running a filter sock stopping this process?

Righteous · Oct 22, 2019

So the math is just a little wrong, but I'm guessing the real problem was in the measurement of phosphate in that test batch.

So if you had added 4g to 4 liters of water and got 2.4ppm, that actually means that each 1g on 1liter would give you the same 2.4ppm.

The issue though is that I believe 4g of KH2PO4 is going to result in a MUCH higher PO4 level in that 4 liters of water than 2.4ppm. Maybe it was so high the Hanna couldn't read it?

Here's a calculator you can use for dosing... if you select DIY you can choose KH2PO4 and then try some calculations.

Righteous · Oct 22, 2019

ooops... forgot the link:

Planted Tank Nutrient Dosing Calculator

EI - Estimative Index, EI daily, EI Low Light / Weekly, PPS Pro - Perpetual Preservation System, PMDD - Poor Man's Dosing / Dupla Drops, Dose to reach a target and Result of your dose.

barrreport.com

surcalation · Oct 22, 2019

Righteous said:
So the math is just a little wrong, but I'm guessing the real problem was in the measurement of phosphate in that test batch.

So if you had added 4g to 4 liters of water and got 2.4ppm, that actually means that each 1g on 1liter would give you the same 2.4ppm.

The issue though is that I believe 4g of KH2PO4 is going to result in a MUCH higher PO4 level in that 4 liters of water than 2.4ppm. Maybe it was so high the Hanna couldn't read it?

Here's a calculator you can use for dosing... if you select DIY you can choose KH2PO4 and then try some calculations.

Maybe the reading was too high but it appears to top out at 2.50ppm. so getting a reading of 2.40ppm is under that.

Using the calculation you posted it's saying I have dosed the tank to 5.40ppm three times. So I think the tank if all things are balanced went up to a reading of 16.2ppm. but that's assuming the Phosphate I being removed via the skimmer as I am not running a sock as my tank isn't set up for one.

Does that seem right?

Righteous · Oct 22, 2019

That calculation is actually for dipotassium phosphate (K2HPO4)... i think you said you used potassium dihydrogen phospate (KH2PO4). But the value is probably still pretty close.

Someone can correct me, but at those levels I think phosphate can get adsorbed into the rock, etc. I would probably keep monitoring the phosphate even after LC additions. Maybe keep GFO on for a good while to make sure any leaching doesn't build up.

Righteous · Oct 22, 2019

Came across this post. Based on this and the calculator, I would assume you dosed around 20ppm phosphate, much of which is now bound to your rocks. I would make sure you keep running GFO. The phosphate will only come out once the phosphate levels in water drop enough.

So you were told your rock leaches phosphates? NOT!

depends on what material it is made ofWhat about man made rock, such as Real Reef rock? Do you think man made rock can leach phosphates?

www.reef2reef.com

surcalation · Oct 22, 2019

Thank you for the replies @Righteous it has been really helpful. So assuming it's about 20ppm after 4 days of Lanthanum Chloride I should be able to get a reading below 3ppm IF it's being bound and coming out in the skimate. If not I suppose I need to put some 10 micron socks on the returns to my refugium some how to get the LC out.

I just want some phosphate left as having no Phosphates got me in this pickle in the first place

If anyone else wants to chime I am more than happy for more collective opinions.