Low Nitrate

[fry_lover]

I have a 48x15x18 very densely planted with lots of floating plants and loads of moss balls, other plants are mostly Onion Plant and Java Fern and all plants thriving. No co2, but x3 tubes, so atleast a decent level of lighting.

Filtration is x1 small external (Aquapro 1) and x2 Fluval 1 internals at the other end (mostly to maintain some water flow throughout the tank)

It's a community tank, livebearers, cory, tetra's, zebra danio's

I have approx 105" of fish, so its heavily stocked, the max according to PFK (Practical Fish Keeping) for a tank this size is 86", so i am technically over stocked.

Usually i would do a 30-35% w/c evey 7-10 days. Normal nitrate readings, after not doing a water change for 10 days would be about 15-20mg/l (my tap water comes out about 25mg/l). I test for ammonia, nitrite, nitrate weekly, mostly out of habit. Never detected ammonia or nitrite in this tank. pH remains a constant 7.8 to 8.0

ANYWAY.... i haven't done a water change for almost 3-weeks now, and i just tested the nitrate and its MAX at 5mg/l and as close to 0.0 as i ever got from a test. My test kit seems fine as tap water came out at the usual 20 mg/l (ish) and my Cichlid tanks were about 40-50 mg/l. And i tested twice and both times was in the 5mg/l range

SO.... my question, obviously i gonna do a w/c as its been 3-weeks, but if my nitrate is this low, what do you think in terms of a routine?

I do use some Seachem plant ferts, so i think that increases the need for water changes?

In a tank with this low a level of nitrate how much water would you change and how often?

 

[rdd1952]

I did a Google search but couldn't find any informtaion on an Aquapro 1 filter so I don't know what the gph rate is on that. The Fluval 1s are only 50 gph so those 2 only give you 100 gph meaning the other filter would need to be about 150 gph to be adaquate. It is very possible that all the plants are using the ammonia before it can be processed into nitrite, thus no nitrate. That still wouldn't explain why the level for the tap is also disappearing. My first guess would be that you have some type nitrate removal sponge or media (such as nitro-zorb or neolite) in your filters that are removing it.

As far as water changes are concerned, nitrate removal isn't the only reason to do them. You also do water changes so can do gravel vacs to remove waste, refill what has evaporated (you shouldn't top off a tank) and just provide clean water in general.

 

[ArauraDiscus]

Are you sure you shook the second nitrate test bottle vigorously for 30 seconds? If not, you will have very low and innacurate levels of nitrate come out in your test.

 

[Bignose]

Plants. Simple as that. You said it yourself that the plants are healthy and growing. The simple fact is that almost all aquatic plants prefer to take up ammonia as their nitrogen source. (Terrestrial plants generally prefer nitrates, though some prefer ammonia, too.) Aquatic plants can actually expend a little energy to convert the nitrates to ammonia for their own use. Well, if your plants are taking up a significant portion of the ammonia your fish are putting out, there isn't much ammonia left over to go through the bacterial colony and cycle. And maybe the plants want the nitrogen so much they are converting some of your tap's nitrate as well. To keep this tank healthy, all you have to do is keep the plants healthy. This is just about as close to nature as you can get in your home.

Now, about water changes, you still want to do them. You need to refresh the buffering and the micronutrients and frankly the fish really just like fresh water... think of how nice it is to open the windows on that first spring day to get fresh air into your house. You also n eed to take out the microtoxiins that get into every tank. Stuff like cigarette smoke, cooking oil, carpet fumes, cleaning fumes, etc. But, you probably don't need to do a significant portion every week. You can probably go to once every two weeks or a little longer.

If you like reading about a tank like yours, I'd recommend reading Diana Walstad's Ecology of the Planted Aquarium where she talks about setting up a planted tank so the plants act like the filter just like in your tank. In her book she says she only changes the water once every few months. I think that's too long, but, maybe not.

 

[fry_lover]

Are you sure you shook the second nitrate test bottle vigorously for 30 seconds? If not, you will have very low and innacurate levels of nitrate come out in your test.

Thanks, well aware of this but you are correct to point it out, i shake both bottles VERY vigourously for about 60 seconds to be sure.

Plants. Simple as that. You said it yourself that the plants are healthy and growing. The simple fact is that almost all aquatic plants prefer to take up ammonia as their nitrogen source. (Terrestrial plants generally prefer nitrates, though some prefer ammonia, too.) Aquatic plants can actually expend a little energy to convert the nitrates to ammonia for their own use. Well, if your plants are taking up a significant portion of the ammonia your fish are putting out, there isn't much ammonia left over to go through the bacterial colony and cycle. And maybe the plants want the nitrogen so much they are converting some of your tap's nitrate as well. To keep this tank healthy, all you have to do is keep the plants healthy. This is just about as close to nature as you can get in your home.Now, about water changes, you still want to do them. You need to refresh the buffering and the micronutrients and frankly the fish really just like fresh water... think of how nice it is to open the windows on that first spring day to get fresh air into your house. You also n eed to take out the microtoxiins that get into every tank. Stuff like cigarette smoke, cooking oil, carpet fumes, cleaning fumes, etc. But, you probably don't need to do a significant portion every week. You can probably go to once every two weeks or a little longer.If you like reading about a tank like yours, I'd recommend reading Diana Walstad's Ecology of the Planted Aquarium where she talks about setting up a planted tank so the plants act like the filter just like in your tank. In her book she says she only changes the water once every few months. I think that's too long, but, maybe not.

Thanks for such a thoughtful and detailed response, yes i have heard of the Walstad stuff and i do like the idea of my plants doing a lot of the filtering