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Cycling tank safe to add fish.

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Hi team,


Have been fishless cycling a tank for a couple of weeks, and kick started this by stealing established sponges from my other tank, dirty gravel, plants etc. 


Was cycling well until pH crashed out, so bought it back up along with some buffer. 


I tested the tank yesterday and got 7.6 pH 2ppm ammonia 5+nitrite and 30ppm nitrates

This was after a small water change to drop the pH slightly as it was sitting at 8.0


I came home from work today (24 hours later) and tested water again and got 7.6ph 0amm 0nitrite and 0nitrate (triple tested using API master kit)

Guessing the cloudiness is bacterial bloom and there's a large amount of biofilm. 


Given the parameters, would it be safe to slowly start adding fish from my other tank (wanting to move my bnp across as this will be there new home). 

I have 3 bnp, but will move them over 1 or 2 at a time to acclimate the tank to bioload. 

See picture for current appearance 


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I’d be hesitant right now. Possibly adding some more ammonia and seeing how fast it disappears. If you’re at the point where it reads 0 ammonia and you’ve built up some nitrates, you may be good. Nitrates are the key. No nitrates, probably not cycled. If it takes longer than 24 hours you’re probably not quite cycled yet. But probably very close. If it clears in a day and you get nitrates, you have a basic cycle. A baby bacteria colony, if you will. You’re safe to add a few fish at this point. Just keep testing daily to make sure the colony can keep up with your fish. Bacteria colonies grow and change depending on the number and size of your fish. A new colony may not quite be able to keep up yet. And you may still see ammonia occasionally. Then water change. add some prime to dechlorinate and you should be good. If you’re able to stay at zero, you can slow your testing to once or twice a week 

Edited by Tony s
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It's very unusual for nitrates to drop from 30 ppm to 0 ppm, especially in a single day.  Your tank doesn't look to have that many plants.  Do you have any Tetra or ACO test strips?  You could double check the various readings with those.  In addition, you might try running the API nitrate test again.


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There is quite a bit of plants in it, just the cloudiness hides a lot..theres 2 small anubias, 5-6 java ferns, some thin valisnera runners that are growing out, a bunch of hygro polyspirma, a bunch of blue stricta and some water sprite

My other tank runs similar levels of plants and is heavily stocked (90l with 8 adult platies, 3 black phantom tetras, 3 juvi yoyo loaches and 2 x 6 inch female bristlenoses and 1 x 3 inch male bristlenose) and that almost never shows a nitrate level. 

I also heavily seeded the filter in the new tank with sponges and gravel from my established tank

 I only have the API test kit, and I know that nitrites will show on the nitrate test so my guess is that was also part of the reading. 

Have just dosed the tank with some food (hard to find straight ammonia here where I am, would need to buy Dr Tim's or frit fishless fuel from Amazon and the shipping is more than they are worth), will watch it over the next 48 hours. 

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