Oreo

I've got a 70gal tank I dosed 2g of dry KNO3 which should have yielded 5ppm in the tank (when considering already present nitrates.) When I tested the water about four hours later it was as if all the KNO3 I added had been used already or something.

Can plants take in over 2g of KNO3 in only several hours? (They had been kept in very low nitrate environment for several weeks. I have been dosing Excel & a liquid trace mix till today when I finally switched to dry ferts.

I've been using a very nice Hach DR2000 spectrophotometer to get precise measurements of the nutrient levels in the tank water.

Anyway, I dosed another 5g of KNO3 to get the level up. I'll test again in the morning.

Oreo

Just measured this morning. Been about 12hrs since I dosed 5g of KNO3 to 70gal and I get a 3.9ppm. So I dosed another 5g. Either I've got some crazy hungry plants or something else is using a lot of nitrates!

For comparison, in those same 12hrs .29ppm of PO4 had been used.

bosmahe1

You must have alot of stem plants. I have had times when I would put 1 gram in a 46 gallon and measure zero nitrates the next day. I've also noticed that 1 gram of KNO3 doesn't disappear as quickly if the plants have had a major trim recently. So maybe plants can suck up that much nitrate. I'm sure that a plant mass weighing and calculation could be used to verify but, that would be to much work.

Oreo

Tested again. Since my last post the plants have used .16ppm of PO4.

Philosophos

I've got a couple ideas that might help. First check "should have" vs. what actually happened. Test your NO3 and PO4 dosing on a small scale in DI water. Moisture does nasty things to dry weights, even the best test kits can fail.

Outside of that, I'd say that if your plants are actually sucking up that much PO4, then the plants are going to be heading for the nitrogen next. Some people limit PO4 to reduce nitrogen uptake on top of reducing NO3 to push their reds higher.

Your NO3 column levels sound low over all; perhaps it's a limiting nutrient, and the plants are starved. Try pushing up to 10-20ppm and see if the uptake backs off after a while.

-Philosophs

Oreo

Thanks for your post.

I suspect the plants have been starved for quite a while. I've been experimenting with a continuous drip water change system. Turns out I reduced the nitrates to almost zero for a while, and was not fertilzing. They have probably had some PO4 available just via the fresh tap water though. Based on what you're saying, that could have contributed to the sharp demand for nitrates.

Philosophos

No problem, hope it helps.

Phosphates come in through food quite heavily as well. Compared to the nitrogen content, most foods have too much PO4.

-Philosophos

Aquaticz

Out of curosity how much was the spectrometer and which water parameters can you test with one/

Thanks