Photosynthetically Induced Phosphate Precipitation

[Floyd R Turbo]

Garf remind me how you get your pH to stay so high all the time?

Also like I mentioned before I have had those chunky bits on the screen/algae mat on my L2 with tank pH below 8.0. So I don't know what that says.

[Garf]

Garf remind me how you get your pH to stay so high all the time?

Also like I mentioned before I have had those chunky bits on the screen/algae mat on my L2 with tank pH below 8.0. So I don't know what that says.

Well, its not high all the time. Im aerating the screen for 4 days, then no bubbles for the last three days. I've got a very slow running sump (about 300 or 400 lts hr), so the scrubbed water recirculates over the screen more than most, which gets the pH to rise. Along with that, Kalk additions increase pH. I had some glistening waxy deposits in between some of the algae strands on the last clean. The day before cleaning, I am running the scrubber lights for 36hrs non stop to keep the pH in the upward direction prior to harvest.

[Garf]

Similar reduction in phos levels this week, barely detectable on the Red Sea test I'm using. This would indicate that i can still run the screen aeration, and increase the "free food" supply for 80% of the time. Harvesting later, then back on with the screen aeration. If I don't get excessive frothing of the sump, this would indicate (to me) that the DOCs have been flocculated and trapped by the screen, or at least turned into particulates (critter food ?) instead of dissolved organics. Doing a 5% per month waterchange to minimise the risk of precipitating out any essential elements from the water column.

[Garf]

BIOGENIC DECALCIFICATION, that's what this precipitation is caused by, and the process by which algaes remove Co2 from bicarbonate, been around a while;

http://www.thekrib.com/Plants/CO2/decalcification.html

[Garf]

Evidence that the increased pH actually binds organics, hence trace metal complexes etc to the precipitation;

http://wap.aslo.org/lo/toc/vol_15/issue_4/0633.pdf

this confirms my observations on my own tank.

Organic compounds may be precipitatcd because the increased pH causes a decrease in their solubility, or they may be removed from solution by association with the few Ca.C03 nuclei that form early in the experiment (Fig. 2.). In either case, organic compounds are removed from solution before rapid CaCOs precipitation occurs

however, if the concentration of organics in the tank is too high, the precipitation does not occur. In cases of rising phos levels, either skimming or activated carbon should be used to reduce organics, therefore allowing the precipitation to occur;

Consequently, rapid CaCOn precipitation does not occur until these organic compounds are removed from solution