Plant Decay and Nitrites

[oscaremmy]

I am a big fan of planting as an aid to fish health through the additional processing of fish waste into nitrates. However, the process depends on plants growing and remaining healthy. I recent set up a 29g community tank with 6 zebra danios and 4 corydoras. Unlike my other 10g planted tanks, I experienced alarming levels of nitrites in this new tank, such that I was forced to add salt in addition to changing 1/3 of the water daily. This had not happened at all with the 10g tanks, even though they were much more densely stocked with fish and had similar substrates and water.

Yesterday my Nitrites (lethal to fish) were hovering around .25 ppm, barely dropping even after a radical water change. Nitrates were 5 ppm and ammonia was 0.

I realized that the hornwort plant in the tank was dying and was literally coming to pieces. As it decayed, it was of course, adding to the bioload with which the biological bacteria were struggling to keep up. I removed the dying plants and as much of the plant debris as I could get. Hey presto, no nitrites, no ammonia, nitrates 5 ppm and building Now my job is to gradually lower kH (16 ppm at present) through smaller water changes using RO water...aiming for 3-6 ppm. The smaller water changes post-cycling will allow pH to fall due to the impact of peat and bogwood. Aiming for about 7.2 pH (8.2 at present). The other tanks are all at 7.2 constantly.

At that point, I can move my 16 harlequin rasboras (in 2 tanks at present, each containing 10 and 6 rasboras) into the 29g tank, giving a total of 26 fish. I may move the two smaller corys from the 29g into one of the vacated 10g tanks, in which there are already 3 established panda corys. That will then be a cory only tank. The final move will give me a total of 24 fish in the 29g tank. I hope to be able to do this in the next 2 weeks, as the 29g plants really start to thrive.

Just wanted to issue this as a warning for new planted tank keepers - plants are only beneficial when they are healthy and growing!:grinyes:

 

[TLT]

Thanks, I didn't know that. Does the decaying plant matter contribute to ammonia too? Or does it not go through that pathway?

 

[Charlie Greiner]

The part many people do not realize is that plants get their food from the water and that, as they grow, the nitrogen compounds they have removed from the water are stored in the plants. When a plant dies, these stored compounds are released back into the water. Also, the plant itself, as an organic entity, decomposes and can cause an increase of harmful compounds. That is why the most successful aquarists using live plants immediately remove dead plant matter and have their systems set up so they harvest living material (pruning) which in turn removes the nitrogen compounds from the tank.

Charlie

 

[OldMan47]

The decaying plant matter does contribute ammonia to the water. If the ammonia processors keep up but the nitrite processors can't you get a nitrite increase.
I am a bit concerned about how you are using RO water. I hope you meant you are going down to 3-6 degrees of hardness from 18. 18 ppm is only about 1 degree of hardness.