iron bonding to phosphate to reduce GSA

hmmm, interesting thought. We're all making guesses. The phosphate is also good for plant growth, roots, and so on.

Yeh I'ts at best a guess i'm quite the ignoramus when it comes to chemistry .I've just always been confounded by promotion of the idea of essentially surplus dosing with nutrients and at the same time claiming the plants are out competing the algae while still having said surplus . The Walstad book offered me attractive logic on that point targeting iron as the preferred limiting factor nutrient in the water column . I't would be nice to get more info on how quickly different proposed high cec substrates take up iron in the water column .Can anybody direct me to test work done in this area please ?

This is another good experiment waiting for someone to try it! Ms Walstad made the statement that algae, not growing on the substrate, can get iron only from the water. And, that iron has to be bioavailable - not bound to a stable anion. But, except for floating plants, all of our plants can get iron from the substrate. That surely suggests that keeping available iron from the water is one way to discourage algae.

For several years I managed to avoid any GSA, and I was always using twice the recommended dosages of phosphate. I was convinced it worked, but I had no idea why it worked. I didn't think of how easy iron and phosphate combine. I have no idea why phosphate didn't inhibit other forms of algae.

Dirt is very high in CEC.

Yeh dirt it's something I tell myself i'll try at some point .This is my first high tech tank .Mostly I do sunlit polyculture (rearing rainbowfish as well) .Ponds with lotus, barclaya longifolia from seed crops ,aponogetons and crinums .I often allow green water cycles in them as it gets rid of most other forms of more destructive algae .Duckweed is also utilised as its root system don't go down and entangle my plants which other aerial plants do .Co2 added with shoddy bell diffusers and aerated at night.

Hi Hoppy,
I thought About the phosphate gsa reduction after looking at my tanks for a while plant less ones as well .I asked myself whether possibly gsa runs on a lower iron threshold than other algae and the addition of phosphate might reduce it down further past its limiting factor threshold ?Any thoughts on that Hoppy ?
Regards Chris

One thing that Ms Walstad said in her book is that Fe+++ ions, the bioavaliable iron, in the water don't remain there except for a short time, because the plants very quickly take them out of the water. That is a clue, but I haven't figured how to use it. One possibility is that Phosphate ions remove the iron ions even faster than the plants can remove it. So, perhaps GSA needs more, not less, iron than other algae forms, so it is GSA that suffers the most when phosphate ions take away the iron ions. I'm not a chemist, even an amateur chemist, so I'm handicapped in thinking about this.

Hi Hoppy,
Came up with that because my Altum angel tank which gets a lot of water changes with largely Ro water has quite a bit of GSA no plants so no ferts .Substrate is supposed to be inert but I am running at low phs 5 to 6.5 so that could be affecting availability of iron .There just shouldn't be much iron in there most water changes I've done on a tank .Still I'm light on test work and heavy on supposition .Started to try to bottle neck the iron in my high tech tank so I'll watch which algae drop of first . They do get fed chicken liver a bit that's got probably more iron than the fish will utilize as a after thought .
Regards Chris