helenf

As I understand it, the idea of a NPT is to have 0 ammonia, 0 nitrite and 0 nitrate, as the plants use the ammonia as it is produced.

What I am wondering is how you know that there is actually enough nitrogen in the tank for the plants to consume?

The potting mix I used as a substrate (beneath gravel) in my NPT didn't release any ammonia, nitrite or nitrate at all into the water. It did release a lot of phosphate, so I guess that macronutrient is available in the soil, but what about nitrogen?

I understand that feeding the fish provides nitrogen to the plants. But how do you know when there is enough nitrogen going into the system?

So far, I have been adding nitrogen to my NPT by doing water changes from a "normal" tank that usually has nitrate levels of 20 or so. The plants in my NPT, presumably mostly the duckweed, make short work of that - a level of 10 goes to nothing in a day or three.

So my my plants can use that much nitrogen, aren't I going to risk having more algae problems by not giving them that much nitrogen in fish food? I am confused about how this works.

I am starting to get algae in the tank (brown, green and hair algae), despite the best efforts of a tiny siamese algae eater, who I have put into the tank temporarily. I don't want the algae to get out of control and I don't want to have to have algae eaters in there permanently (certainly not SAEs, which grow much too large for sure). So I've got to get the nutrients in balance better than I have so far, which means I need to understand how these tanks works rather better than I do.

If anyone can explain this thing about how to provide enough and yet not too much nitrogen for the plants, that would be great!

Thanks.

mistergreen

Yes, adding fish food will give you NO3 though NH3 (ammonia).
Maybe your Nitrate test kit is off (happens all the time) and there might be 1 or 2 ppm of NO3 in your tank.

A good indicator of nitrogen deficiency is when you notice your plant leaves dying, turning an off color and is stunted.

If that happens, You can cheat and add seachem's nitrogen or KNO3.

yum

so is it possible to be too heavily planted? some of plant leaves are starting to have holes and turn a bit yellowish. i have a bit of a hair algae outbreak and was wondering the same thing.

Tony65

By adding change water from another tank aren't you constantly destabilising the NPT tank?

It's just like you are adding 20 ppm nitrate fertiliser each time but without balancing it, unlike the NPT fish-food route which is low-key and stable/balanced.

Your NPT plants have probably got used to the minimal nitrogen regime - dumping nitrogen in via a water change probably just feeds the algae?

helenf

Why would adding nitrogen that is immediately available to the plants, in the form of nitrate, be more unstable than adding it in the form of fish food, where it isn't immediately available to the plants?

I certainly don't add enough 20ppm water to bump the ppm in my NPT tank to 20. It's more like 5ppm. But I'm confused by this because reading general planted forums has given me the impression that your ideal nitrate level for a planted tank is 10-15ppm, so the plants always have some nitrogen available. So I don't understand how this matches up with the NPT ideals, where supposedly the plants are the most important thing, but we're not feeding them as much as other people say is ideal.

I've also been told, and it makes sense, that there shouldn't be fish food decaying on the floor of the tank, though I should overfeed (but I don't understand by how much, and how you can overfeed without ending up with decaying food beats me) and that I shouldn't overstock, but that I should plant heavily.

It seems to me that planting heavily without overfeeding or adding some other source of nutrients for the plants, will end up with badly growing plants, and let more algae into the tank. But since NPTs clearly work, and can work very well, its clear to me that there is something I'm misunderstanding here.

So if anyone can help me to clear up my confusion, that would be great.

mistergreen

NPT are generally refered to as LOW-tech tanks, meaning that the light levels are low but get a little boost here and there with sunlight...

When light levels are low, plants don't take up that much nutrients so having 1-5ppm of NO3 is perfectly normal... That's how it is in the real world/wild too.

I also keep a HIGH-tech tank and I keep NO3 around 10-15ppm because plants in consistant high light situations take up much more nutrients.

makes sense?

THe difference between a High-tech and a low-tech concerning plants is the speed of growth.. That's all.

And don't forget about other nutrients NPK, micros & CARBON which is the other part of the equation.

YUM: your problem is low in potassium.. You might want to add Potassium.. I do that sometimes to my NPT... I've notice that NPT's are generally too low in K.

dwalstad

I'll make a stab at clearing up confusion about Nitrogen.

You assume that your plants are nitrogen deficient, because the nitrates quickly disappear after you add them. Right?

However, you have discounted denitrifying bacteria. I suspect that bacteria (not plants) in your NPT are quickly reducing the nitrate levels. Denitrification is a major nitrate removal process in NPTs (see my book, pp 63-64), especially in one like yours with potting mix, which is highly organic. Soil bacteria use nitrates as a substitute for oxygen under anaerobic conditions. That is, they breath with nitrates, so nitrates are going to disappear very, very fast in your tank.

Now, nitrogen is readily available in NPTs. Every time the fish respires, it is giving off ammonia from its gills. The ultimate source of this nitrogen is fishfood, but it doesn't take long for fishfood proteins to go to ammonia. Not long at all!

Plants love ammonia. They'll sponge it out of the water in excess of what they need. You may never measure nitrogen in your tank. Unless your plants turn completely yellow (not just new growth), then I would stop chasing this "red herring" and relax about nitrogen. This is the one nutrient that is almost always adequate for plant needs in NPTs. Rejoice that you don't have ammonia and nitrite problems.

I would look in other directions (lighting, water hardness, etc) to address the fact that some of your new plants have holes in the leaves (could be calcium deficiency, snails, etc). If one or two species is getting holes and doing poorly, while others are doing okay, that's to be expected. For this, I would remove the dying plants and maybe try some other plant species.

If ALL your plants aren't doing well in a new tank with potting mix, then your tank has a true problem.

kekon

I have a high-tech tank but it seems to me nitrogen deficiency doesn't necessary shows as yellowing on old leaves. I have issues with chlorosis on new leaves each time there is at least 20 ppm of potassium in the water. When K is lower chlorosis disappears. This is not Fe, Mn or any other micronutrient deficiency. It suggests that magnesium is blocked by higher K amounts but it's not the case - after adding more and more Mg nothing was improved. Only after adding more N the situation somewhat improved but it's still far from perfect and i'm really confused of what needs to be done to make plants to have rich colors.

dwalstad

Scientists have repeatedly shown the direct competition between potassium and ammonia uptake in aquatic plants. So excessive K, which is what you've got with 20 ppm, could indeed, block ammonia uptake and induce nitrogen deficiency. Some plants are more susceptible than others.

Yellow leaves can also be due to metal toxicity, H2S toxicity, ect.

Since you're keeping a high-tech tank, future questions on this would be better addressed to the people that actually keep high-tech tanks. They're the ones that should know what the side effects are to adding excessive K fertilizer and how to get plants "to make rich colors". In NPTs, the goals are much less ambitious-- healthy plants and fish, and low-maintenance.