Photosynthetically Induced Phosphate Precipitation

[Garf]

Firstly, I would like to thank "BILK" for putting me onto this idea.

Had this flying around in my head for a few days now, and found a link that confirms my thoughts;


http://www.patentgenius.com/patent/5851398.html


It appears that at around a pH of 8.5 (needs to be tested), phosphate will precipitate out of solution, perhaps with some calcium. In normal tank conditions with a pH of higher than 8.5, the precipitate causes a nutrient sink somewhere in the tank. When the pH is then reduced, by bacterial production of Co2 for example, the phosphate is released once again, and the cycle continues.


Be aware that the scrubber screen increases pH at the algae surface through Co2 depletion.


The theory is if the water being processed by the screen has a pH slightly lower than the precipitation pH of phosphate (8.5 ish), the increase in pH on the algae due to photosynthesis will precipitate phosphate ONTO the algae cells for removal when harvesting the algae.


It may be that some scrubbers require no fiddling with to facilitate this (they may be the ones with magical phosphate removal properties). I suggest MOST scrubbers could be improved with regards to phos removal.


I have started to test this by allowing my sump to increase pH to 8.3ish. Of course this means removing my air flow to the screen. My phos level has been almost static for months now, so I should notice any difference easily.

After doing a few searches on this, it seems it's a well known phenomena, which I think should be followed up.

[Floyd R Turbo]

This could be interesting.

[celtic_fox]

So if that turns out to be true, is the moral of the story to harvest Algae during (or etter yet, at at the end) of the light cycle?

[Garf]

Yes, but the screen pH must be above the precipitation pH, whilst the water feed to it must be below the precipitation pH. It may be that the flow over the screen is as important as the intensity of the light in this regard.

[Ace25]

Makes me glad I run my tanks in the 7.8-8.0 pH range. Just tested on the screen, below the screen, and in the next chamber in my sump, all read 8.01 right now.

[Garf]

Makes me glad I run my tanks in the 7.8-8.0 pH range. Just tested on the screen, below the screen, and in the next chamber in my sump, all read 8.01 right now.

Mine is normally just higher than that @ 8.1 to 8.2 and the scrubber is keeping everything static at the minute, with N&P not going up or down. I'm thinking that if this does work, the phos concentration could be manipulated. Lots of people report phos increasing and this may (may not!) have a benefit. It also appears that this effect may be subject to DOC levels in the water also as it competes with the phosphate somehow (perhaps another cause of increasing phos), dunno, I'm not a scientist . Willing to have a go and see what happens though.

Edit - Its the pH on the algae cell interface with the water that's important in relationship with the water flowing over the algae, if you catch my drift.

[BearHill]

woaw .. Im intrigued! I will be stalking this post! Thanks for sharing!

[sklywag]

Will this be posted in the "Scrubbers for dummies" section?

[Garf]

Progress so far - 48 hrs ago, removed the screen aeration. 24 hrs ago, stopped skimmer operation. pH has increased to 8.4 in the sump and have had a 1 DKH alkalinity decrease, so put some bicarbonate in. No magical phosphate drop yet, early days though.

[tebo]

Hi Garf, Is nothing new that I've never had problems with phosphate, in fact converse one here again, in my case the problem was no3

It turns out that my tank has always had a pH above 8.4, in fact the swing is between 8.46 and 8.52, this can be the explanation of why I have no problems phosphate

my phosphates never rise more than 0.01ppm and why I'm fed full since I have few fish and I want to bring up some hard corals

regards