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Good morning folks. I'm reaching out to see if anyone has a rule of thumb regarding how much time you would expect it to take for the Nitrates to go down if you were to stop feeding your fish. I have a cycled system with ample plants and appropriately size bio mass, etc. and I'm running into high nitrate levels even after having stopped feeding my fish. Water is clear, ammonia is trace, nitrites are 0, and all other perimeters are optimal.  My thought is that maybe my grow beds have accumulated waist that is breaking down continually but I have a solids filter and it is cleaned regularly. 

Thanks  

 

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Hi Jejanov

 "my rule of thumb" is water change. Mainly for the fish health/welfare.  

Of course fish age/specie means there is a variety of tolerance to high nitrate, but it can take weeks to reduce the nitrate levels.

So I would recommend to use some of your tank water in the garden, and then top up the tank.

I assume your "fresh water" source, does not hold a high nitrate level ?    

 

                                             

cheers

Edited by ande (see edit history)

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Thanks for the reference.  I’ve been doing substantial water changes and have been successful in reducing the nitrate levels to 40 ppm only for them to climb back up to 100 with a reduced feeding. I’m going to look at sourcing lower protein content feed. Plant growth is abundant and healthy  but obviously the nitrate production is exceeding the uptake. This will be an even larger problem over winter. 

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Hi Jejanov, 

Maybe you may need to add another grow bed and add some more plants in that grow bed. I wouldn't be doing to many more water changes, you may effect the chemistry of your already matured system. I'd be testing my water daily and logging it, doing maybe 10 percent water changes every week or two now and gradually work on settling and bringing the nitrates down as well as adding another grow bed. I know your system is mature but I wouldn't be to bothered if my nitrates were 100 even 180 at the moment and depending on your fish, as I suggested I'd just work on gradually trying to even them out and gradually reducing them to the levels you want.

A couple of questions,

How long have you stopped feeding your fish for?

How old is your system?

What's your pH?

What's your fish tank water temp?

What plants are you growing and What type of fish do you have?

Cheers.

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This instruction video isn't correct. The fishfood should cover the needs of the fish as accurate as possible. Shifting to a lower protein diet (sub-optimal) is going to result in more waste, lower food utilization % (higher FCR), and maybe even compromised fish health, thus this makes no sense to me. IMO better would be lower total feed load, less fish or more plants and/ or secondary nitrate removal. Water replace, dnf etc..

Btw if you stop feeding the organic waste in your system will still be broken down slowly, further bacteria mass will go down too, again with the release of nitrate, thus there can be a long delay in reduction of nitrate production after reducing input.

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