Zero phosphate - should I believe my test?

[SteveM]

I have been slowly converting from silk to real plants over the past month or so, and after reading all I could find on algae, it seemed that I might have excess phosphates. So now I have procured a Hagen PO4 test kit, and I measure a big fat 0ppm. Is this likely to be correct or do I have a bad test kit? I have performed the test twice, with the same result - I'm not an idiot, so be assured I followed the directions

The tank is 75G, with 4 GF (2" to 4"), a BN plec (2.5") and a Black Mystery Snail. There are 5-6 small aponogetons (Wal-Mart bulbs), all of which are sending leaves to the water surface, a Red Melon Sword, and a few bunches of Hornwort which I have placed in the gravel (not floating). I generally perform a 20-25% water change every 1-2 weeks. Lighting is Coralife 2x65 freshwater aqualight, mounted on those little legs. No CO2 injection - I'm not ready to go quite that far on this yet.

Water params are:
PO4 = 0ppm ???
NO3 = 7.5ppm (between 5 and 10)
pH = 7.1
GH = 2
Alkalinity = 40ppm
Temp = 70F

The algae is not really bad, but it is a constant presence. The BN plec takes care of it for the most part on the leafy plants, but the hornwort seems to get a permanent algae coating after 2-3 weeks in the tank. I guess he's not interested in cleaning bristle by bristle.

So I guess my question is really what should I be doing next? I hadn't expected to find low phosphate levels, but if that is actually the case, I guess I need to start dosing phosphate? From what I can gather my Nitrate levels are even a little low for the plants - should I be adding some of that as well? Anything else I should be pouring into the tank?

Maybe I just need more fish?

 

[malkore]

Hagen is at the bottom of my list (with RedSea) for reliable test kits.

While it is possible, I bet you have some phosphates, that a SeaChem or Salifert kit would detect.

you also don't really have enough Alkalinity to safely inject CO2. 3dKh is the minimum, which is 54ppm. You'd need to add a little baking soda to raise the Kh to 60-70ppm (to give yourself a little extra buffering)

 

[SteveM]

Went out and got some fleet enema and made up a 1ppm test solution, and the Hagen PO4 test kit read it right at 1.0ppm. So I guess the 0ppm is real, at least to the extent that I have < 0.25ppm since that is the lowest color on the scale.

Time to give the tank an enema I guess - 10:1 nitrate to phosphate is the standard ratio for the plants, right?

 

[travis simonson]

That works well. 1 ppm PO4 is what I run mine at, although some prefer it to be .5 ppm while others run theirs around 1.5-2.0 ppm, so I think 1 ppm is definitely in the safe range.

 

[malkore]

Yeah, 10:1 is a pretty common ratio. some go 20:1, others 15;1, some 5:1 (though I don't recommend it unless you know what you're doing)

 

[SteveM]

I'll start with 0.5ppm PO4 and see how things look in a few days.

Thanks for the responses - sometimes it helps to get that direct feedback, even if you've already read the answer in 100 older posts. I'ts a tough change of mindset to start adding things that you used to be trying to minimize when it was fish only :? I'm still not sure I'll be able to bring myself to add nitrates if it comes to that.

 

[malkore]

Steve,
If it makes you feel any better, a virtual colleuge of mine, Steve Hampton, has actually purposely overdosed a tank to create various forms of algae, so he could write up an article about combating algae, and what he did to fix the problem he created. Just remember it can take several weeks to fully wipe out any algae.
If the algae is fading, you're doing the right things, and its just a matter of being patient.