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Zero Nitrate all across the boards - Seaweed?

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Now this is not a question - as this sub forum might suggest - but rather a statement which I am very excited about.

I am not quite sure where to post it, because it concerns water quality, food fed, and of course the importance of maintenance.


As you will find out quickly all my tanks are overstocked. This topic is NOT about advocating that over-stocking is fine. It is if you can deal with it but if you can keep goldfish without overstocking, then stick to NO overstocking. This is just my personal experience which involves over stocked goldfish.



Just recently I posted a topic about control testing the nitrate test of the API Freshwater Master Test Kit, because I  keep getting 0 nitrate when testing my tanks.

And for those newer ones of you who don't know my years of fish keeping: all of my tanks are stocked at about 200+% recommended capacity. However, instead of the 50% weekly water changes per 100% recommended capacity I do twice weekly 85% water changes - which is about triple water changing compared to normal standards. I keep all tanks bare bottom with a decent amount of anubias, and on average 15x filtration.
Filters are cleaned out every couple months but I try to not do all of one tank in one go, but do one of each tank every other week etc.


So to get back to that topic I had posted about how to control test my nitrate test, I ended up stuffing a hand full of basic potting soil into a stocking and letting it soak in a cup of spring water for 12 hours, after which I then ran the water through a coffee filter to remove most of the soil, and then tested it.


Below is the comparison between my 55g with currently 8 fish between 5 and 11 inches length - all single tails - where the last water change happened four days before the testing. The fish were not starved; they were fed twice daily with once pellets and once dried seaweed.


I do wonder if feeding the seaweed - which is actually quite high in protein and makes a great main food for these fish - is part of the reason why less nitrate is the end product. With it being in a way so much more natural than feeding them food that contains grains and additives, although obviously not a native food source to wild goldfish, it also has improved the color on some of the fish a lot. But maybe it causes them to produce less ammonia as waste product, which in the end means less nitrate.
Also I keep a lot of shubunkins and "sakuras" and can really tell when the white heads and fin bases turn yellow from the sea weed.

But ever since I started making this about half of their main diet, I also have less floating issues in those food sensitive, improved growth and color, and now apparently better water quality.

The picture below shows the test result of my tank/s (the same for all of them) on the left vs the deep red result of the potting soil water on the right.
Years ago I would used to get 20-40ppm between those water changes with "only" 5 fish in a 55g but ever since I changed the food a couple years back, the test result has gotten pale golden yellow showing 0 nitrate.






And also to put this out there, it is the same result in all my 6 tanks. Almost all of them are by Koko's standard quite overstocked.
Not that those standards are wrong, because they are awesome. I only have them overstocked because I could not find good enough homes for my home bred fish and decided that they would be better off in my extreme care than handing them over to some shady pet store.

Edited by Oerba Yun Fang
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In a cycled tank, the amount of nitrate produced depends on the "crude protein" in the food.  Unless you virtually starve the fish, nitrate gets produced.  Nitrate can get removed from the tank water by plants, algae, or denitrifying bacteria.  


If you had enough plants in your tanks to use all of the nitrate, you certainly would have mentioned it.  An established pond with no plants in the system often has little nitrate because the algae growing over every underwater surface use it up.  If you had this situation, you would notice it because you could only see your fish from the top.


That leaves denitrifiers -- a very diverse group of bacteria and archaea that live under anaerobic, aerobic, and anoxic conditions and produce various products from nitrate.  The most common denitrifiers in aquaria thrive under anoxic conditions.  Anoxic means in low levels of oxygen.  These can grow just below the surface of a gravel layer.  Nitrifiers, which need a lot of oxygen, live on the surface of the gravel.  Because they use so much oxygen, the layer just below them has little oxygen (and a supply of nitrate from nitrification), an ideal situation for anoxic denitrifiers that can grow to a population level that uses all of the nitrate produced in the tank.


Dirty filters make another choice growing space for anoxic denitrifiers.  Many large pond filters have anoxic spaces where denitrification occurs.  

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