Plants and Nitrates - Fact or Fiction

[ddavis1979]

Does having a panted tank actually reduce nitrates? I feel like I have heard somewhere that plants help to absorb nitrates in the water, but I wanted to verify that rumor?

[Cermet]

Plants use nitrates as food.

The issue is the amount.

A very dense plant growth will use a lot of nitrates but the average aquarium with only a few plants will not use enough to make any difference compared to the nitrates produced by the fish (via the bacteria in the filter.)

That all said plants only use nitrates at the best rate with enough lighting and trace nutrients and, of course, enough CO2. For a low density tank, CO2 and many trace nutrients are already available in the tap water (but often one or two trace nutrients are in short supply. A good reason to dose a liquid fert from time, to time.)

Plants do not easily consume ammonia or nitrites and at high levels these waste products can harm plants - so cycling with plants needs to be done carefully - levels should not be allowed to get too high (another good reason to use a 1 - 2 ppm ammonia level for cycling.)

[Cliff]

Plants mostly consume nitrates and phosphates. Those are two ingrediants in most plants ferts. I do not beleive the amount they consume would be very impactful to your water quality tho, at least not in a low tech planted tank.

I have had my 90 gallon set up without plants, and then added a lot of low light, low demanding plants that grew like weeds turning my tank into a heavy planted tank. I did not notice any changes in my nitrates. I am sure they are consuming nitrates and phosphates, just not enough for it to show on my API test kit as most time the kit barely even shows 5 ppm. The stocking and maintenance routines stayed the same.

I have not kept a high-tech planted tank before (higher light levels, CO2 and ferts) so I can not speak to those types of set-ups

[KevinVA]

I can confirm what Cliff is saying. My 75gal heavily planted tank, which has low-med lighting w/ low-med light plants does not consume a great deal of nitrates. I always have between 5-10ppm (sometimes 20) and am required to perform the necessary water changes per week to bring that down to about 5ppm.

My 10gal high-light w/ low-high light plants consumes almost every bit of nitrates. I will also say that it depends on the plant. If it's a fast growing plant, chances are that it will consume more nitrates. Slower, much less. For instance... I have 2 Amazon swords in my 10, but I didn't notice a huge change in nitrates until I added 2 Dwarf Lillies. Now I regularly have 0-5ppm weekly.

[Lady Hobbs]

Agree with all posters above. I have to add nitrates about 3 times a week because I'd have 0 nitrates without it. But I would not expect nitrates of 80 to be reduced by having plants, either. That's what water changes are for. But to get technical, a planted tank is really a tank fairly full of plants. Some will add one little plant to a tank and call it planted and it's no more a planted tank than one radish plant is a garden.

:)

[KingFisher]

I have a heavily planted 90g with high lighting and my nitrates never are above 10. Fast growers suck up a lot of nitrates. Many with high tech planted tanks actually have to dose nitrates because their plants use up more of it than their fish can provide. Like the others have mentioned, there has to be a balance of nutrients present in order for this to happen.


Waterchanges are still necessary whether or not your plants are absorbing the nitrates. Plants do not take the place of a good routine maintenance schedule.

[ddavis1979]

Good to know. Yeah I have a very lightly planted tank, and my nitrates hover between 20 and 30 ppm at the end of a 10-14day time period where I normally do a 30% water change.

However, I have been adding more plants as time continues forward, and I wanted to know what to expect, if anything.

Hypothetically speaking, if you have a heavily planted tank, where your plants consume large amounts of nitrates as well as detritus off the bottom, what does a water change buy you in terms of water quality?

[Honey Badger 1]

If you set up the tank with a good amount of plants, you would not notice how much nitrates the plants are consuming because they have always been there and unless you took the plants out and tested again in a few days you really don't know how much nitrates they are consuming. Plants use nitrates and they use a decent amount, that is why many people with heavily planted and stocked tanks have 0 or near 0 nitrates. I am not talking about a couple plants, I mean a moderate to heavy planted tank.

If you put more plants in your tank you would still need to do the same amount of water changes to replenish trace minerals the fish need to be healthy and remove hormones they produce.

[KingFisher]

Waterchanges do a lot more that remove nitrates. There is also fish hormones and other dissolved solids that we do not test for. They also replenish electrolytes that fish need.

[Cermet]

Your nitrates are rather high - they should always be below 20 ppm and better still, below 10 ppm. Also, what is the nitrate level of the tap water, if any? In a low tech tank, adding some plants will do little for the nitrate level - most likely the fish are producing waste far faster than what the average mod/low level lighted plants can consume. You need to do weekly water changes assuming the nitrate level of the tap is below 5 ppm.