Phoshate, Kalkwasser and Cyano - Could Kalk be fueling my Cyano Problem

[Reefdom]

I've been thinking, mainly due to a cyano problem on my sand bed and a little on my rocks.

We know Kalk precipitates out phosphate into Calcium Phosphate (exact mechanism is unclear) and renders it inaccessible to corals, possibly algae and maybe cyano???

Some will be removed by the skimmer but some will circulate and settle out in the substrate.

Does cyano have the ability to pull the phosphate out of calcium phosphate? If so it could have the monopoly on phosphates, allowing very easy proliferation.

I have little algae, have done for a good few weeks now,high ph, which may help phosphate precipitation, and low residual phosphate in the water, yet cyano seems to have no problem spreading.

Coral growth is good, colours are good.

Any thoughts from those with a better understanding than myself?

 

[Lasse]

Does cyano have the ability to pull the phosphate out of calcium phosphate? If so it could have the monopoly on phosphates, allowing very easy proliferation.

IMO - it is exactly this that will happens below the mats if NO3 levels is very low and forming of sulfur hydrogen will take place - but my theories is just mine

I have little algae, have done for a good few weeks now,high ph, which may help phosphate precipitation, and low residual phosphate in the water, yet cyano seems to have no problem spreading.

Low phosphate in the water column (below 0.03) will IMO limit micro algae forming on sand and rocks - giving a free space for cyanobacteria/dinoflagellates to establish themselves

Sincerely Lasse

 

[Reefdom]

I think your theory is now shared by myself.

The mat allows localised ph to drop, which in turns allows the calcium phosphate bonds to be broken and uptake of phosphate by the cyano bacteria.

I have po4 levels in the water of 0-0.02 Enough for coral growth to be good and colours to be good but not enough for competition.

I have searched for days to find some reasoning behind what i am seeing in my tank or some one else that could explain this.

Thank you very much for your quick response. I may turn off my kalk stirrer for a while and see what happens unless there is a way to keep running it and avoid this issue i am seeing.

 

[Lasse]

I would dose PO4 up to around 0.05 - 0.1 until the cyanobacteria have disappeared - after that slowly tune it down to around 0.05. also keep the NO3 around 5 - 10 ppm as long as you have this problem.

Sincerely Lasse

 

[Reefdom]

I've tried, as soon as i add any po4 or no3 the cyan takes off even faster.

i guess identifying what is contributing to this problem is a start.

I've removed the kalk stirrer for now so i can monitor my nutrient levels etc.

I will give it a week and then dose some po4 if necessary. it may be that without the kalk phospate rises anyway. If not i have kno3 and potassium phosphate from my old planted tank days i can use.

Thanks for your help, i really appreciate it.

 

[Randy Holmes-Farley]

I'm not convinced the kalkwasser is a substantial part of that theory. The "we all know" part is weak, IMO, and the idea that it is settling out on the sand and driving cyano is not clear cut either.

That said, phosphate binds to sand regardless of kalkwasser use, so that part of the theory certainly is plausible.

 

[Reefdom]

I’ve read a few articles that point towards kalk reducing phosphate although the exact mechanism is unclear.

I do understand phosphate will precipitate out on sand regardless but if ph is high, and kalk is being dropped, will phosphate precipitation not be even higher?

Is localised ph a thing? The theory behind phosphate precipitation at the point of kalk dripping into water supports this so a cyano mat reducing ph beneath it due to bacteria respiration would work the same? If there is a higher than normal po4 precipitated in the sand due to the scenario above will this bit aid the cyano?

I’m far from a scientist, chemist or anything between or around. I’m just trying to straighten my thoughts.

That’s why I posted here

 

[Lasse]

In an experiment I did with freshwater phytoplankton - i did measurements of pH and free phosphate every hour during day. It was a locked system with no influx what ever. I did it in two different system. The water was - as we say in Sweden - of the hard water type - it means that it contain for freshwater very high values of calcium - up to saturation level.

What I saw in this experiment was a very close relationship between pH and phosphate content. When pH was high (up to 10) - PO4 was near zero - when pH was low (down to 7.5) PO4 was higher and this was repeated day after day. Light schedule was light on for 12 hours - light off for 12 hours. I´m sorry to say that we did not measure the calcium content in the water. I did this experiment back in 1996 and I´m sorry to say - i have not keep the notes. For measurements we used professional equipment.

Sincerely Lasse

 

[Reefdom]

Very interesting observation.

Perhaps there is more to be discovered in the relationship between phosphate, calcium and ph. Or maybe I just have not found anything.

In my head it makes sense but that doesn’t count for much and I’m sure there are other factors at play.

It will certainly be interesting if I register a po4 reading in the morning after returning 0-3 ppb everyday over the past week.

I may test po4 daily this week to see if anything changes and I’ll be watching ph too.

 

[Randy Holmes-Farley]

I’ve read a few articles that point towards kalk reducing phosphate although the exact mechanism is unclear.

I do understand phosphate will precipitate out on sand regardless but if ph is high, and kalk is being dropped, will phosphate precipitation not be even higher?

Is localised ph a thing? The theory behind phosphate precipitation at the point of kalk dripping into water supports this so a cyano mat reducing ph beneath it due to bacteria respiration would work the same? If there is a higher than normal po4 precipitated in the sand due to the scenario above will this bit aid the cyano?

I’m far from a scientist, chemist or anything between or around. I’m just trying to straighten my thoughts.

That’s why I posted here

This is a fine theory, but I do not think there is, at present, convincing evidence that it happens.

I’ve written about the effect of kalkwasser or other high pH additives on phosphate. I agree it is possible that calcium phosphate forms, but there is no experimental evidence for it as we use kalkwasser. If it did form, it might redissolve even at normal tank pH (like magnesium hydroxide does after high pH additions).

On the other hand, phosphate binding to aragonite from seawater is established fact, and may partly explain the growth of algae and bacterial mats and sand. Peak binding is around pH 8.6 in seawater, dropping off in either side of that pH.

 

[Randy Holmes-Farley]

Perhaps there is more to be discovered in the relationship between phosphate, calcium and ph. Or maybe I just have not found anything.

I think those relationships are completely understood from an equilibrium solubility standpoint.

Some aspects of how fast precipitation and dissolution happen at a given pH, calcium level, and phosphate level are not well understood.

 

[Reefdom]

Thsnks Randy. Funnily enough my ph peaks at 8.6 at the end if my high ligh period. I’ve been unable to find anything that says if ph this high is good it bad so I left it be.

Perhaps ph that high was causing peak rates of phosphate binding.

Turning of my kalk stirrer might help reduce phosphate binding rates due to reduced ph rather than anything else.

 

[Lasse]

I think those relationships are completely understood from an equilibrium solubility standpoint.

Some aspects of how fast precipitation and dissolution happen at a given pH, calcium level, and phosphate level are not well understood.

Free calcium is sometimes used in wastewater treatment in order to precipitate phosphorus. pH is critical in these plants. See this explanation

Sincerely Lasse

 

[Randy Holmes-Farley]

Free calcium is sometimes used in wastewater treatment in order to precipitate phosphorus. pH is critical in these plants. See this explanation

Sincerely Lasse

yes, I agree that is true. Does it impact something I said?

 

[Lasse]

Does it impact something I said?

I maybe misunderstand you and I´m sorry that i dig up an old thread - when I answer - I did not see that it was from 2020. But I´ll think that the thread starter @Reefdom have interesting approach - what´s happens below the cyanobacteria mats according to release of phosphate from the sediments.

Sincerely Lasse

 

[arafas]

I'm not convinced the kalkwasser is a substantial part of that theory. The "we all know" part is weak, IMO, and the idea that it is settling out on the sand and driving cyano is not clear cut either.

That said, phosphate binds to sand regardless of kalkwasser use, so that part of the theory certainly is plausible.

Randy can you explain a little more about kalkwasser and phosphate. Is having high Ph not using kalk will strip phosphate vs using kalk and stripping phosphate. What is more beneficial, using 2 part and having high Ph let's say with co2 vs kalk and having high ph

 

[Lasse]

Whats stripping the phosphate out of the water is the forming of calcium phosphate, hence extra calcium ions will make the method better IMO.

Sincerely Lasse

 

[Randy Holmes-Farley]

Randy can you explain a little more about kalkwasser and phosphate. Is having high Ph not using kalk will strip phosphate vs using kalk and stripping phosphate. What is more beneficial, using 2 part and having high Ph let's say with co2 vs kalk and having high ph

Strip is a bit of a strong term for the process, but here are some thoughts.

When limewater (kalkwasser) is added, the local pH and alk and calcium at the point of addition is quite high, especially pH that could easily be over pH 9 locally at the point of addition. That can drive processes such as calcium phosphate precipitation that may not happen in the tank overall, even if the tank pH is on the high side (say, pH 8.5).

On the other hand, having high pH overall does tend to increase the chances of having abiotic pecipitation of calcium carbonate on warm surfaces such as heaters and pump impellers, and also on existing calcium carbonate surfaces such as sand. Freshly precipitated calcium carbonate will tend to bind some phosphate. Hence, having higher pH will tend to reduce phosphate for this reason. How large that effect is is not clear, but I expect it is substantial in tanks with a lot of precipitation.

 

[arafas]

Strip is a bit of a strong term for the process, but here are some thoughts.

When limewater (kalkwasser) is added, the local pH and alk and calcium at the point of addition is quite high, especially pH that could easily be over pH 9 locally at the point of addition. That can drive processes such as calcium phosphate precipitation that may not happen in the tank overall, even if the tank pH is on the high side (say, pH 8.5).

On the other hand, having high pH overall does tend to increase the chances of having abiotic pecipitation of calcium carbonate on warm surfaces such as heaters and pump impellers, and also on existing calcium carbonate surfaces such as sand. Freshly precipitated calcium carbonate will tend to bind some phosphate. Hence, having higher pH will tend to reduce phosphate for this reason. How large that effect is is not clear, but I expect it is substantial in tanks with a lot of precipitation.

Thank you. Another question. Coralline algae, so my previous tanks with live rock and such I had crazy coralline algae growth. In my current setup running high Ph in this case using esv 2 part and co2 scrubber to keep my paremeters in check. Ph well above 8.3 in day time. I haven't seen much of coralline algae, only some spots here and there. my phosphate on hanna url checker read 0.03 and always had been that way, even with ICP analysis. I have been in the hobby over 15 years and I have never struggled to have coralline algae. Some people don't care for it since it can over take things and they need to do more scrapping, but in my over the years experience I belive coralline is a good thriving tank. Any thoughts on this? Basically hence my previous question about kalkwasser, would it help with coralline better then 2 part?

 

[Randy Holmes-Farley]

I do not think we have a good handle on why coralline thrives in some tanks and not others, but I have always thought tht higher pH, lower phosphate (say, 0.03-0.05 ppm) and higher magnesium (say, 1400 ppm) are likely to be desirable.