Bmitchell486 554 Posted January 28, 2017 I have a water chemistry question about Nitrates. History: My 72 has been set up for almost 7 years. I've got 6 goldfish in there, overstocked. I've got 3 ryukins that are almost 7 years old, and are 6 inches (including their long tails). The other 3 are ranchu -- one is 4.5 inches, one is 3 inches, and one is 2.5 inches (including tails). My maintenance routine: I change ~80% of water once a week. I service the filter (rinse out all media in a bucket of tank water) every 6-10 weeks. I regularly test my water (API Master Kit), typically once a week right before I do my water change. Occasionally I spot check my pH bc I'm curious to see how it fluctuates throughout the day. Food: They get repashy gel food 1-2X a day. They get bloodworms 4-5 times a week. They can't have any pellets anymore because it makes one of my old fish float, and it makes another one of my old fish bottom sit. My question: Why, in the ~3 years since I've regularly tested my water, have I never seen a reading of Nitrates? About 6 months ago, I let my tank go for 2 whole weeks without a water change, continued feeding regularly, and my nitrates read 0. I decided to do this experiment again -- I just went 3 weeks without a water change, tested my water this morning and nitrates are zero. I following the testing instructions exactly, and the kit is newer. Keep in mind, I fully understand that there is plenty of organic waste that builds up and that Nitrate is just one type. Any waste build up is bad, not just Nitrate. I kept a close eye on my fish the whole time, they remained active, no bottom sitting or pouting. Their behavior has remained perfectly normal. I am sure there is organic waste built up after 3 weeks of no water changes, but why are my Nitrates still 0?!?! I've read conversations online where someone says "My goldfish is sick, my tank in cycled, my ammonia/nitrite/nitrate is 0, what's wrong?" And the response I typically see from at least 1 responder is "A cycled tank never has a nitrate reading of 0. Zero nitrates means your tank is not cycled. You should always see a nitrate reading." So am I missing something? Thanks in advance for reading! Just looking to learn. 0 Quote Share this post Link to post Share on other sites
Bmitchell486 554 Posted January 28, 2017 Sidenote - I've seen ~5 PPM Nitrate reading a few times in my pond since it was set up last spring. I'm just talking about my 72 in this thread. 0 Quote Share this post Link to post Share on other sites
shakaho 6,312 Posted January 29, 2017 Well, if you saw someone on here say that a cycled tank never has 0 nitrates, you should have also seen my vigorous objection. You have zero nitrates in your tank because you have denitrifying bacteria in your system. Denitrifying bacteria can be found just below the surface of substrate, in sumps that have collected some muck in the bottom, and in filters -- particularly dirty filters. Although microbiologists have just started realizing the diversity of denitrifying bacteria, the ones most commonly found in fish tanks and small ponds thrive under anoxic (low oxygen) conditions, ideally close to nitrifiers that "feed" them nitrate and also lower the oxygen concentration to the levels they prefer -- just a little bit. In substrate, the nitrifiers live in the surface area where they find a good oxygen supply and lots of ammonia from the fish. The denitrifiers live just below them in an area of low oxygen and abundant nitrate which they convert to nitrogen-containing gases, ideally to nitrogen gas. In a filter, particularly one with a lot of debris caught, denitrifiers can live in anoxic pockets, surrounded by the biofilm that contains nitrifiers making nitrate for them. The bigger the filter and the less often it gets clean, the more likely it will support a stable population of denitrifiers. A well-established pond with a nice big biofilter usually has little to no nitrate. This usually gets blamed on plants and algae using the nitrate, but you can find the same nitrate levels in some ponds with no plants and clear water. Denitrifiers. In contrast, look at a koi pond with state-of-the-art filtration. Virtually every speck of debris gets removed from the water by the seive before it gets to the highly aerated moving bed biofilter. Then it may go to a shower before it returns to the pond. The water comes out clearer than tap water, but it accumulates nitrate just like an aquarium. No denitrifiers in all that high-oxygen water. This review article, while rather old, has a lot of good information on denitrification. 0 Quote Share this post Link to post Share on other sites