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FAQs on Marine Freshwater Quality involving Nitrates: Science

Related Articles: Nitrates in Freshwater Aquariums, Establishing Cycling, Freshwater Filtration, Know Your Filter Media, A Concise Guide to Your Options by Neale Monks, Setting up a Freshwater Aquarium, Tips for BeginnersWater Quality and Freshwater Aquariums

Related FAQs: Nitrates 1, Nitrates 2, & FAQs on FW Nitrates: Importance, Measure, Sources, Control, Chemical Filtrants, Troubleshooting/Fixing, & Ammonia, FW Nitrites, Biological Filtration, Freshwater Nutrient Cycling, Establishing Cycling 1,

Nitrate is broken down by anaerobic bacteria, such as those that live in live rock (in marine aquaria) or stagnant mud (in ponds). It is not easy to create these conditions in a freshwater aquarium, so denitrification (the breakdown of nitrate to nitrogen gas) rarely takes place quickly enough in freshwater tanks to make any difference. Neale

Nitrate...      10/6/17
For Neale Monks and Bob Fenner
Hello again friends,
I’d appreciate your comments and reasoning about a question involving lowering nitrate. I will start by saying that I understand that nitrate like ammonia and nitrite is toxic to fish, though at much different levels/exposures and depending upon species or age of the fish (fry being more susceptible) [please correct me if I am incorrect here or anywhere else].
<This is correct; though the mechanisms, pathways if you will, for poisoning/toxicity of these nitrogenous compounds are different. NO3 in particular can be accommodated; i.e. much higher concentrations can be tolerated with long exposure>
Consequently, if one discovers nitrate levels in an aquarium are high, say 160 ppm [I am using an actual case from my work on TFF, and this is a stable state not something sudden], immediately reducing the nitrate to safe levels (under 20 ppm) is not in itself going to harm fish.
<Usually; yes>
I have been challenged on this, with the suggestion that the nitrate should be lowered gradually over days or weeks, similar to other adjustments.
<Mmm; no. Immediately lowering NO3 concentration is advised>
The idea apparently is that “old tank syndrome” is dangerous and rapid changes can be fatal; but I would respond that the danger with this is due more to pH, and ammonia being ammonium in acidic water and the sudden change to basic pH (pH shock, plus ammonium converting to ammonia) is the problem, not nitrates decreasing. My argument is that nitrate is not like other adjustments (GH, pH, temperature, or whatever) and being toxic the sooner it is lowered the better.
<I concur>
I maintain that any toxin in the water, be it ammonia, nitrite, very high nitrate, substances released from wood or rock that are detrimentally affecting fish, etc, are best corrected rapidly via significant water changes.
Comments please, with thanks.
Byron Hosking.
<Will ask Neale for his separate response here. Bob Fenner>
Re: For Neale Monks and Bob Fenner: Nitrate         10/7/17

Byron, Bob,
I don’t have any real insight into this. But I do wonder if there are differences between species and when comparing marine with freshwater fish. My point being that generalist freshwater fish are able to handle bigger water chemistry changes than more specialist species (or most marines) given they’d be exposed to such in the wild. For example, the pH of a pond can vary between around 7 to as high as 9 once photosynthesis kicks in and dissolved CO2 is used up.
<A useful point/speculation. I do think there are differences between salt/fresh, young/old, acclimated and not species, specimens. Have been to public aquariums that fed huge amounts of food to very large animals... that had thousands of PPM of NO3>
I’ve read before that the idea we can meaningfully acclimate fish to slight pH changes is actually erroneous anyway. The “float them in a bag for an hour” or “drip water into a bucket for an hour” approaches sound good, but supposedly the actual physiology works far more slowly than this. So for fish to actually adapt their blood chemistry (or whatever) actually takes far longer, and what we’re really dealing with is the degree to which fish can tolerate abrupt changes (i.e., shock) and then slowly adjust across days or weeks. Does this sound familiar to either of you?
<Yes; it does>
I do believe, Byron, that there’s a hierarchy of stress factors, and sometimes to minimise a severe stress (such as nitrite, ammonia or extremes of temperature) you may have to increase a mild stress (such as small pH or hardness changes) simply through doing water changes. Of course the standard advice should remain that water changes need to be made with water as similar to the conditions in the tank as practical.
So far as I know, nitrate toxicity hasn’t really been studied across a wide range of ornamental freshwater fish, but experimentally with things like goldfish you really do need quite high levels (100+ mg/l) to cause immediate health issues. In such situations, I think doing moderate water changes across a few days, rather than one giant water change, might be safer in terms of minimising sudden pH, temperature or hardness changes. But that said, if the new water was similar enough to the old, doing 90% water changes has been demonstrated to be perfectly safe in and of itself.
Anyway, keep me posted with what you learn!
Cheers, Neale
<And you, BobF>
Re: For Neale Monks and Bob Fenner        10/7/17

Thanks Neale and Bob.
So what I take from both of you is that with the proviso that parameters (GH, KH, pH , temperature) are close enough to be called the same, a large water change to reduce nitrate from 160 ppm down to 10 or 20 ppm is not going to harm the fish, and is more advisable than doing smaller changes over weeks. I will assume my understanding is correct unless you say different.
<This is a good summation>
I do appreciate the benefit of your experience and knowledge on these issues.
<Welcome. BobF>
Re: For Neale Monks and Bob Fenner    /Neale        10/7/17

I would 100% agree with this.
Triage of any kind is about balancing the big dangers against the minor stresses.
Cheers, Neale

Nitrate/baby guppy problem 05/29/09
Hi Crew, it's me again....
We have a nitrate problem in our 28 gallon.
<Nitrate is best removed from freshwater tanks simply by [a] not overfeeding the fish; [b] not overcrowding the aquarium; and [c] doing more water changes. Fast-growing floating plants are also good at using up nitrate, but that should be viewed as a supplement to frequent water changes, not an alternative.>
Our ammonia is at 0, nitrite 20 mg/l, nitrate 40...so the pet store recommended a bacterial supplement that claims to be 'for fresh and saltwater aquariums'. Will this work?
<No. Nitrate is broken down by anaerobic bacteria, such as those that live in live rock (in marine aquaria) or stagnant mud (in ponds). It is not easy to create these conditions in a freshwater aquarium, so denitrification (the breakdown of nitrate to nitrogen gas) rarely takes place quickly enough in freshwater tanks to make any difference.>
We have a male Betta, my only remaining Neon Tetra, 3 Glo-Fish, 3 Giant Danios, and an African Dwarf Frog. Our 10 Ghost shrimp and 5 Mystery snails all died...and my Betta, who used to easily eat 20-30 pellets (!) a day, now only gets 4 or 5..those giant Danios...:)But anyway he's usually a bundle of energy and now he's lethargic and fights with his own reflection.  Plus his eyes look clouded. We got him almost 7 months ago so could these be age-related cataracts? And my baby guppies (they were born on April 7th) are in the 2.78 L, there's only 2 of them and both look pregnant. One just died...so should I move them to the 28-gallon in a breeder net with our nitrate level?
<I can't see Guppy fry doing well in 2.78 litres of water. Seriously, that's not an aquarium; it's a soda bottle.>
Yes, we have live plants-Umbrella, Amazon Sword, Peacock Fern, Aqua Fern, and White Ribbon. The Amazon Sword ones-and only those ones-are dying. Why?
<Probably not enough light. Umbrella Plant (Spathiphyllum wallisii), Peacock Fern (Selaginella willdenovii), Aqua Fern (Trichomanes javanicum) and White Ribbon Plant (Dracaena spp.) are all non-aquatic plants that will die kept underwater within a few months. Any retailer who sold you these was CONNING you out of money. So I wouldn't trust him/her on anything.  There are many retailers who sell these plants to inexperienced fishkeepers. These plants ALWAYS die and NEVER last for long underwater.  Total waste of money. The reason they "look" healthy is that their leaves are stiff, being adapted to living on land where gravity is more of an issue than underwater. So it takes a long time for them to look dead. But
DIE THEY WILL. Take them out, put them in houseplant soil, and stick them on a windowsill. Enjoy them for what they are: houseplants! As for your Amazon Sword, these are demanding plants that need strong lighting (at least 2 watts per gallon, ideally 3 or more watts per gallon) and a rich
substrate containing iron and other minerals; plain gravel will not do!  Usually when people fail to grow these plants, it's because [a] there isn't enough light; and [b] they stuck the plants into plain gravel without considering their need for fertilizer.>
Please help...
<Cheers, Neale.>

Water readings always zero, Not a bad thing 8/29/07 I'm so sorry for having yet another question. I love your sight, but for everything I learn I have questions. I find the answer and then that leads to more questions. <The learning process.> This concerns water quality. I've got 5 aquariums. I split up the percentage and do daily water changes vs. a large weekly water change. The fish don't even notice as it's syphoned out and slowly pumped back in with a tiny pump from the stored aerated well water. I've done this for over a year and the fish are very healthy. In researching your site for ideas in setting up a drip system (been wanting to do that for awhile) I came across a references stating low level nitrAtes were needed in the water. It happened to be talking about saltwater tanks. Is that true for *only saltwater? <In some very specific situations this is mostly true, heavily planted tank in FW and some clam tanks in SW will benefit from low levels of nitrates, but for most aquariums if your nitrates are 0 then be happy.> My ammonia, nitrItes and nitrAtes have literally always read '0' on my FW tanks (cycled). All the references about nitrAte always say to keep them under about 20-25 for FW fish. So....does that mean I'm *supposed to have at least some nitrates in the water? I always thought I was doing the right thing but I've found sometimes I try too hard and come to find I've over-done it. <0 is best in most situations, just most people are not willing to do the amount of water changes you do to achieve that.> Now I wonder if there's some electrolyte or mineral or some weird alien nutrient I hadn't considered that I'm depriving them of by keeping their nitrates at '0' instead of letting them build up to 10 or 15 ppm. <Nope> I'm so sorry if this is a ridiculous question, I've been pondering it for 3 days. It might help someone else to know this, too. Thank you for your endless patience. I'd gladly join your team and answer questions but I feel I know so little compared to your crew. Mitzi <Don't underestimate your knowledge. When you feel ready, drop a line, we are always looking for people who are willing to help.> <Chris>

Nitrate and the freshwater tank 5/12/06 <Hello> Yesterday I tore down my 29 G FW tank, removing the UGF. I replaced the gravel with eco-complete, and planted the tank. I kept the  power filter in place.  My fishes are in another tank I have, awaiting the trip back to their newly planted home.  This morning I checked my water parameters, expecting all zeros, but see that I have 15ppm nitrates. How is this possible? The one thing I know that concerns me, is my power filter, sat with water  in it, but not turned on,  for 3 or so hours, maybe some bacteria  died?  Would that have an effect? Is the remedy merely a water change, or am I going to have to re cycle. I have no ammonia in there at present. Thanks for your time, soooooo much! Karen <In a freshwater tank nitrate is the end product of the nitrogen cycle, so seeing some is not uncommon.  If you left water in the tank while taking out the gravel it is probably from material released in the cleaning.  Otherwise it could be from dying material on the new plants and planting material.  Either way 15ppm isn't that bad for a freshwater tank, and a water change or two should take care of it.> <Chris>

Nitrate levels in goldfish water Hello all ,      1st off can I thank you for providing all the info and help on the site, it's a great source of info. I have had my freshwater aquarium for about 4 months now and have never had any problems at all, I only have 2 Orandas and they have loads and  loads of room , but when I cleaned out the other day as I always do , I  carried out the water checks the day after only to find unusually high nitrate  levels (7mg/l). <This is actually not high at all... Most goldfish systems have a few to many tens of mg/l of NO3> I cant seem to get it down , the fish seem fine and I have cut the feeding down but I don't know what products to use (don't want to buy any old stuff recommended buy the brain dead 17 year old puppy sales person at the only pet superstore near by) is there any thing you can recommend please. thanks Rik. <No worries... just keep up doing what you're doing. Bob Fenner>

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