I have been having nitrate issues the last couple of weeks.
60 gallon tank
too many fish
almost 300 gallons worth of filtration
nitrates 40+ ppm
nitrite 0 ppm
ammonia 0 ppm

i did a 30 percent water change, and the nitrate levels barely dropped. same results when i did a 50 percent water change a couple days later.
it has been a while since i cleaned the filters, over a month since i changed out the cartridges.
could filters with excess fish waste/ leftover food in them cause nitrates to rise excessively?
I know i have an overstocked tank, and this is probably the cause, but i was curious about how much a dirty filter could contribute...

Best thing i have done for nitrates is live plants. They are amazing. I also do large water changes. I change about 75 percent, refill the water, and then do it again right after. That nearly resets that nitrates. Although it can be a lot of work.

sorry i dont think that i answered your question with my previous post.

well if there is much crap in the filter then the bacterias have plenty of food and wont consume everything. That sounds the most logic to me atleast

bowhunter wrote:

dirty filters do contribute for the increase in nitrate due to
restricted flow of water but bacteria in it can still process
the more lethal elements which are ammonia and nitrite:

yes, i agree with bowhunter. plants something like this;



or this make the difference:

well if i understand the nitrogen cycle correctly, nitrites and ammonia are waste products from the fish eating/breathing/pooping. then beneficial bacteria consume/convert nitrite and ammonia into nitrate.
so if this is correct, then i have plenty of good bacteria getting rid of the nitrite/ammonia.
so having extra food particles and feces in the filter might create even more nitrite/ammonia for the bacteria to turn into nitrates.
the main reason i am suspecting dirty filters is because i stopped feeding for a couple of days, and did a 50 percent water change. i tested the water again the next day to find that the nitrate levels hadn't dropped much if any.

yes indeed it is. but too much nitrate could also stress
the fishes, thus, w/c should be carried out to lower it.

and if there is too much ammonia for the bacteria to handle you could get ammonia and nitrite spikes.

Thor84 wrote:


as above, you are correct for most but last bit wrong. your understanding of the cycle is correct, but the dirty filter idea is wrong. dirty filters will start to produce a slower rater and you will end up with ammonia/nitrites in your readings. there are 3 main ways to lower nitrates

1st and most easy solution is limit your stock and do regular water changes. because your fish stock is smaller a wkly water change of 20% should do. if you are over stocked you will need to do more water changes to cope with the large stock depending on how many fish you have will determine how many water changes you will need to do.

2nd is as said change more water, more often, most people would not like this so it quickly fails as you could end up changing many gallons each day.

3rd is plants. this fails because the amount of plants needed to cope with all that nitrate means you can't see the fish. your tank needs to be packed with plants to cope with the large amounts of poo that large overstocked tanks produce. it will however help a little to lower your nitrates.

if your tank is correctly stocked you should be able to lower your nitrates by a 20-30% water change a wk. That said there is also the possibility that your tap water contains high nitrates so please test your tap water.

thank you marcus. and believe it or not, i tested the tap water for nitrates after my last water change did not have the desired results. 0 nitrates in the tap water. but this was a couple of days after the waterchange was performed.
here in the last month the neighbours have been adding on to their house (and having to mess with the water lines). and while this was going on i noticed the water smelling like sulphur. i don't know if it is related or not, but you never know.
is it possible that nitrates will drop on their own after a while? i tested the 60 gallon again last night after posting this, and they were below 40, where as a day after my last water change they were above 40. weird

nitrates will not drop by themselves it will only go up, the answer is lots of plants or less fish or more water change. its a battle all fish owners have, i myself was overstocked for a while. I was changing 200L every 3-4 days. its just too much work to make fish keeping fun and enjoyable. we all want more fish so the only answer to have more fish is a larger tank, but this still means mass water changes. I keep meaning to visit the London aquarium to see how they cope. i cant see them pumping 2000gallons a wk )))))

hmm, must have been user error then