Why test for Phosphates?

When somebody has an algae problem, they will often say that my Phosphate levels are zero, at which point somebody replies, they are there but the algae is what is using them up which is why the test shows 0.

Then if you don't have any algae problem, then chances are you don't have a Phosphate problem and they will still show as 0.

So is it worth throwing money at Phosphate test kit, when it seems to me they will always read 0?

 

IMO the answer is no. The kits we buy cannot read low enough to detect the amount of po4 that can still cause issues. The test kits test for only 1 compound, inorganic. Leaving organic undetected.

 

Yes it is. The test kit will usually give you a hint that phospahtes are present, if you see algae present then its a good bet you will read something, because unless you have a tank full of algae they can't eat it all. They do gobble up some, but you should still see it in the test.

 

Absolutely yes! I use my Hanna phosphate tester 1-2 times a week! I can monitor my phosphates this way. My tank functions best at around .02ppm of po4 so if I am count in at .01 or "undetectable" on the meter then I up feedings. Then when I see my po4 start creeping above .06ppm I know my gfo is about exhausted.

Strict phosphate control is essential to longevity and heathiness of a reef (if not immediately, you will see why after po4 slowly builds up over the years)

 

Look, the only way you will ever test positive for phosphate is if there is some sort of limitation. If you have sufficient nitrate, iron, other trace elements, light, surface area etc... all the phosphate will be consumed by algae and other organisms. If there is a limitation of nitrate, iron, other trace elements, light, surface area etc... then the algae and other organisms can't use all the phosphate and it will accumulate.

So, with regards to algae, yeah, a phosphate test kit isn't necessarily that useful. However, algae isn't the only issue with phosphate. Phosphate will interfere with coral calcification, slowing down the growth of hard corals and making their skeletons softer and brittler. This is bad and seems to start to occur around .03 ppm PO4. So, using a good phosphate test kit can be help a bit, as their detection threshold at least gets close to this range. So, if you have detectable PO4, with a good test kit, your in trouble... Time to switch out the GFO as Dingo said.

 

Excellent thanks for the replies, so my best bet is to get the Hanna digital test as this will give me a reading that I might not see with a visual test kit?

I am new to this hobby, so the information I gathered in my original post, was the sort of things I deduced from reading other threads, that's why I thought I would ask the question. OK, I shall order one of those, thanks again

 

There are a lot of "ifs" being left out... po4 is more of a problem for stoney corals. If you don't have any, not much of a problem. Algae is a problem... if you have a lot, you have po4. No point in testing for po4 unless you plan on controlling it. Once you learn how to test for it and control it... you will find you no longer need to test for it.

Hobby kits are all low resolution tests... they only give you gross readings. If they indicate any po4... then you don't need a test to tell you you have po4... your tank full of algae is enough. all those people that say they test and have zero... do not actually have zero.

Merck and Tunze make very high resolution kits... they are expensive. They are difficult to read on the low end. PO4 becomes a problem as low as .02... algae can still grow fine at .01

The Hanna check can read that low... yet the error range is plus +/-.04... so sure it can read that low, but what does that mean if the error range is twice what is bad? There are plenty though that are reasonable knowledgeable on the subject and find the accuracy to be pretty good.

 

Algae can grow with no Phophate reading. The clean water algae.
Algal genus Spotlight: Bryopsis "hair algae" - Reef Central Online Community
Sorry about the link to RC, its the best description.

 

Absolutely yes! I use my Hanna phosphate tester 1-2 times a week! I can monitor my phosphates this way. My tank functions best at around .02ppm of po4 so if I am count in at .01 or "undetectable" on the meter then I up feedings. Then when I see my po4 start creeping above .06ppm I know my gfo is about exhausted.

Strict phosphate control is essential to longevity and heathiness of a reef (if not immediately, you will see why after po4 slowly builds up over the years)


+1 Dingo, I read an article that basically said same thing. Your tank functions good with .02 phos. The article was saying you had to balance the phos. and nitrate in a system. If one or the other got out of balance then you would get an algea problem. They never stated what the balance was because it was different for every tank.

 

I think with most macro algae like gha, chaeto, calupera, etc. It is a 4:1 ratio between nitrateo4. Where nitrate is usually the limiting factor here because it takes 4 nitrates to be absorbed per 1 phosphate in growth.
At one point in time when I was really big into growing all kinds of macros I was to the point where I was nitrate limited so I would add potassium nitrate (KNO3) in very small amounts. This served two purposes: one it allowed my cool macros to grow by supplying nitrate, and two it worked to drive my phosphates even lower.
I was accomplishing very low over all po4 without using gfo this way... More of a 100% natural reduction technique.