Why do water changes to control algae when reading 0 P04/NO3?

[smande00]

Slightly random question as I'm not currently battling any algae, but I've read on multiple occasions that even if you're testing undetectable levels of nitrate and phosphate that you should do a large water change anyways because the algae is capable of consuming those nutrients almost as soon as it enters the water.

What I don't understand is how a water change fixes anything in this scenario. If the levels are zero then changing out the water isn't exporting anything other than maybe detritus? What's the point? Seems like if the levels are at zero you should focus on not allowing them to rise from there (ie control the source via food reduction, etc).

[Tang Salad]

This is a good question and the answer is that those levels are never actually at zero, despite what test kits may say. If algae is actively growing, increasing in quantity over time, then you can be certain that there's enough N/P in the water to fuel that growth. The algae could not grow without it! So assuming one is using high-quality RODI water and salt mix, then water changes will decrease N/P, even if the test kits say there was none to begin with.

I haven't tested N or P in many years because algae lets me know when those numbers are increasing and coral coloration (particularly SPS) tells me when they've gotten too low. I wouldn't suggest anyone else go this route unless they're comfortable with it.

[tmz]

Large water changes aren't needed unless a serious nutrie nt or toxic condition affecting the animals in th tank needs a quick correction. All in all the potential for upsetting element balances , water parameters as well macro and microfuana outweighs the benefits a large change may offer,imo.


Water chages are largely ineffective as an ongoing stragtegy for nutrient management in any case. Balancing inputs primarily from food and outputs(filtration, skimming adsorbents, bacterial activity,et alia) is the way to do that.

Watercahnges are important for what they put in ( major, minor and trace elements) and maintaining ionic balances; not so much fo what they take out. I strongly prefer small regular water changes.

[smande00]

Ahh ok - I can buy that.

New question (and no I'm not trying to be contrary, just genuinely curious): What's the point of testing if algae is capable of being fueled at levels below what we can test for and therefore could act as "free" test (no algae, no detectable levels). Are there other limiting factors (assuming lights are kept on) for algae growth?

[smande00]

Large water changes aren't needed unless a serious nutrie nt or toxic condition affecting the animals in th tank needs a quick correction. All in all the potential for upsetting element balances , water parameters as well macro and microfuana outweighs the benefits a large change may offer,imo.


Water chages are largely ineffective as an ongoing stragtegy for nutrient management in any case. Balancing inputs primarily from food and outputs(filtration, skimming adsorbents, bacterial activity,et alia) is the way to do that.

Watercahnges are important for what they put in ( major, minor and trace elements) and maintaining ionic balances; not so much fo what they take out. I strongly prefer small regular water changes.

That had kind of always been what I had thought changes were for as well. Mostly to get stuff back IN to the water. Using it as a reduction means for something that already was testing as extremely low was what wasn't clicking for me.

[tmz]

The point of testing is to determine whether or not the nutrient input and output balance in an aquarium needs adjustment.
Keeping dissolved nitrogen(ammonia, nitrite, nitrate) and inorganic phosphate(PO4 species) low in the water column will limit nuisance algae. Less to assimilate equals less algae when all is said and done . High levels of phosphate and dissolved inorganic nitrogen not only fuel algae and other pests but can be harmful to corals and other invertebrates, in terms of calcification and zooxanthelae growth.

Some species of algae are less sensitive to specific nutrient limitations than others and some may be able to gather up organic sources of nitrogen and phosphorus making it all a bit more complex. Further substrate and rock exposed to high PO4 may leach some back for months fueling algae on their surfaces for months after levels in the water are reduced .
However, ime, persistent efforts to keep PO4 under .03 ppm or so and NO3 under 1ppm ultimately result in very little nuisance algae in the tank.

[smande00]

The point of testing is to determine whether or not the nutrient input and output balance in an aquarium needs adjustment.
Keeping dissolved nitrogen(ammonia, nitrite, nitrate) and inorganic phosphate(PO4 species) low in the water column will limit nuisance algae. Less to assimilate equals less algae when all is said and done . High levels of phosphate and dissolved inorganic nitrogen not only fuel algae and other pests but can be harmful to corals and other invertebrates, in terms of calcification and zooxanthelae growth.

Some species of algae are less sensitive to specific nutrient limitations than others and some may be able to gather up organic sources of nitrogen and phosphorus making it all a bit more complex. Further substrate and rock exposed to high PO4 may leach some back for months fueling algae on their surfaces for months after levels in the water are reduced .
However, ime, persistent efforts to keep PO4 under .03 ppm or so and NO3 under 1ppm ultimately result in very little nuisance algae in the tank.

Completely understand that high levels of PO4 & NO3 are toxic to different life forms in the tank and I'm definitely not advocating no testing (because obviously years and years of folks' experience supports this).

I guess what I was trying to get at is that if levels of PO4/NO3 that register 0 on a test kit are truely enough to fuel growth shouldn't that (the growth) be an even better indicator than testing, giving you an earlier warning than if you waited for the levels to become high enough to actually register?

I feel like I'm missing part of the equation somehow. I know folks are able to register readings like your .03 ppm for phosphate and don't have problematic algae growth so there's got to be something other than undetectable levels of PO4/NO3 that allow it to get out of control. Otherwise wouldn't you have seen signs of algae before you were able to register that reading?

The only thing I can think of is that the algae must already have to have a pretty good foothold in the system before it's able to absorb those nutrients faster than you can register them on a test? In which case regular testing would show a steady rise in levels prior to an outbreak until some critical mass of algae growth is reached and consumption begins to outstrip the nutrient import and levels fallback down below registerable levels?

[tmz]

Maybe it's a foothold or maybe it's just a localized source like: a wet and dry filter with bioballs contributing nitrates , detritus buildups ,PO4 leaching substrate ;algae that's using organic phospahte that doesn't register on the test or algae that is less limited by a dearth of a particfular waterborne nutrient than other types are.

En masse,however, algae growth will wane when levels of bioavaliable nitrogen and inrganic phospahte are low and will increase when they are high. Green hair algae and phytoplankton is particulary limited by low PO4.
Using alge gowth by undefined species( ther are thousands) in variable localized conditions by its growth or lack of it is at best and only sometimes a very imprecise way of predicting the acutal dissolved inorganic nitrogen or inorganic phospahte in the water available for other oganisms. All it tells me is that algae is growing or it's not growing. Testing ,even hobby grade testing with limited pecision tells me what's in the water.

[smande00]

Good stuff.... I appreciate the patience and perspective, thanks! Always plenty of stuff to learn in this hobby.

[tmz]

You are welcome.

[bertoni]

I agree that water changes typically don't work well for nutrient control. In some cases, though, the water column might have enough organic debris for a water change to be worthwhile. Remember that our test kits can only detect certain forms of nutrients, so they can't always just the total nutrient content of the water content, just what's currently mineralized.

In the case of phosphate meters and kits, they are not all that accurate down in the 0.02 ppm range or so, which isn't surprising, given the low concentration.

Testing can be useful in some cases. If the phosphate level is very high, for example, that might alter the approach taken. GFO might need to be changed very often, or maybe a switch to lanthanum chloride would be more cost-effective.