Question about phosphate and algae

[ScottJ]

I see this statement often in threads about nuisance algae and low phosphate test results;

" The algae is consuming your phosphates and you are getting a false reading."

I get how that might happen, but how would you get a correct reading, or confirm that is indeed the case and high phosphate is fueling algae growth?
If the statement is true and you have algae, good or bad, in any significant amount, wouldn't a phosphate test be useless?

Just wondering is all.

 

[YOYOYOReefer]

Your hypothesis is correct... hobbiest grade test kits will not measure the bound phosphates.

 

[Reefahholic]

I see this statement often in threads about nuisance algae and low phosphate test results;

" The algae is consuming your phosphates and you are getting a false reading."

I get how that might happen, but how would you get a correct reading, or confirm that is indeed the case and high phosphate is fueling algae growth?
If the statement is true and you have algae, good or bad, in any significant amount, wouldn't a phosphate test be useless?

Just wondering is all.

I think a good Phosphorus ULR test is always good to perform. If it’s reading zero and you have a lot of algae, you can bet PO4 is present for the algae to grow. It’s the same when you have a wall to wall tank full of SPS colonies. A lot of the time you get zero readings, but you can look at the corals and tell by their color that phosphate is indeed present. We probably need to be able to measure in PPT (Trillion) to see what’s really going on.

 

[Clown2020]

From personal experience this can be true of both nitrate and phosphate to an extent. I had an alge explosion due to feeding way too much coral food and amino acids on top. My phosphate reading and nitrate never went up. However after cutting way back the alge reduced

on their own the test kit results may not be that useful but combined with other results and observations can still provide useful insights.

 

[jda]

The only real way to get a correct reading is to get a good tool like Hannah Ultra Low. Then, realize that even 1 or 2 ppb is enough to not growth limit algae. It will grow with very little in the water column. The algae can sometimes have higher concentrations in places more proximate to a source, like dry/dead rock that often is bound with terrestrial phosphate that can take years to unbind.

 

[YOYOYOReefer]

the real way to get a reading for phosphates bound in the rocks involves boiling the rocks in nitric acid as step 1, not exactly reef friendly.

 

[Dan_P]

I see this statement often in threads about nuisance algae and low phosphate test results;

" The algae is consuming your phosphates and you are getting a false reading."

I get how that might happen, but how would you get a correct reading, or confirm that is indeed the case and high phosphate is fueling algae growth?
If the statement is true and you have algae, good or bad, in any significant amount, wouldn't a phosphate test be useless?

Just wondering is all.

If someone believes PO4 in the water causes nuisance algae growth, then that person needs a reason for why there is nuisance algae growing when there is low measurable PO4 in the water.

A much simpler hypothesis is that algae grows in an aquarium because it is not being eaten or physically removed. Forget the nutrient arguements.

 

[jda]

^ so true. I have 1-3ppb of P and about .1 of N (need ICP to test it) and algae would grow like crazy if I did not have urchins and snails. Also, if you starve macro algae you can also harm micro algae in your corals (dinos/zoox).

 

[Garf]

Algae scrubbers can be grown in most nutrient levels even if no algae is evident in the display. The difference between display and scrubber screen is herbivory and substrate maturity (I include coral, coralline cover in that).

 

[Timfish]

I totally agree with the OP. To add to the complexity of the problem we can't test organic and particualte forms of phosphorus so even if we could quantify how much inorganic phosphorus (PO4, orthophsohpate) is in a system and is being used by the life in the system we still wouldn't have a complete picture.

Phosphorus metabolism of reef organisms with algal symbionts

https://esajournals.onlinelibrary.wiley.com/doi/abs/10.1002/ecm.1217?casa_token=ziDzrEEJ8g0AAAAA%3AHnfuGTIntMdqOtx2ij-lnoTh7qVg8VBhYFz98e60zfBEvx5IcIVGhmlpUYmzIJuqUNVm0sG8_0vth6lq

Fig 4

 

[Garf]

Bacteria can work on detritus to release inorganic phos in the local area. Bacteria can be energy deficient, so feed on the sugars released by the algae in exudates, which in turn traps more detritus. Quite a nice arrangement, and little if any of it shows up on a phosphate test kit.

 

[jda]

Even if you cannot test for all of it, which is fine, at least understand the relationship that P has with aragonite. The rock and sand can/will bind huge amounts if you keep adding and adding it. Eventually they will not be able to do the hard work anymore and your water levels will rise quickly. The aragonite can act like a buffer (good) at low levels or a reservoir (bad) at high levels. Don't be eager to add P to your tank like so many people do (it is not a good idea even though some of the internet mob thinks that it is) and keep up the export even when levels are low.

Just like feeding your fish produces ammonia/ammonium for the corals to get nitrogen from (not nitrate), they also produce several form of phosphate/phosphorous which is also helpful to a variety of things (not just the one that people dose or test for). So feed your fish well and export well. This has worked for a long time. Availability > residual levels.