Vanishing nitrate

[ianclick]

Ok So heres the thing.

Any ideas why a tank that has been cycled for over 2 years would suddenly start showing a marked drop in nitates?

180 litre tank 420mm length x 200mm width x 180mm depth, fortnightly 20% water changes, daily spot cleaning, 2 juvenile & 2 adult axolotls, No live plants, consistent readings over the last 22 months ammonia 0, nitrites 0, nitrates 20-40 ppm. Two x 80 litre per min diffused waterfall filters rinsed every second water change.

In fact nothing has changed with the tank except the nitrate level. I have another tank same size same shape same number of axolotls and stable parameters so I'm stumped. Nitrates in the tank are now reading less than 5 ppm

Any ideas

 

[Jacquie]

Hi Ian,

Just a thought. Has the pH level in that tank dropped?

An extract from the Caudata Culture Article 'Cycling an Aquarium for Aquatic Animals':

"As a final warning, pay close attention to the pH in long-term aquariums, as the pH tends to drop over time in old aquariums (the nitrification process is an acidic process). If the pH drops too low, the biological filter will crash."

 

[Darkmaverick]

Hi Ian,

I think Jacq is on to something here. I immediately thought of the proportion of beneficial bacteria in the tank (nitrifiers etc), and what could have caused the change, in a long standing well established tank. I know the bacteria population is affected by the pH of the environment but i overlooked that nitrification is an acidic process. I really think its worthwhile checking the pH of both tanks you got and see if there is a difference.

Cheers.

 

[SludgeMunkey]

Yes, sounds like a pH drop to me also.

 

[tran]

Do you have any anaerobic spots in your tank (deep sand, porous rocks, etc.) that would grow denitrifying bacteria which causes the chemical reduction of nitrate (NO3-) to nitrogen gas (N2)?

Denitrification in aquaria generally take much more than half a year to develop so maybe that's why you are suddenly seeing a drop in nitrates after your tank has been established. If this is the case then that is good news.

 

[Darkmaverick]

That is a good thought Tran, very deserving of more green "pixie dust" points. However, i think with Ianclick's long experience with axie tanks, i really doubt he uses porous rocks or deep sand substrates considering he often dishes out the very same advice to new members. Nontheless, a vital point that is worth mentioning.

Cheers

 

[tran]

Hi Rayson, I wasn't insinuating that Ian was not experienced. On the contrary, this natural nitrate removal process is something many aquarium enthusiasts hope and pray for (salt water tanks sometimes have deep sand beds >6" to achieve this). But it's hard to develop these anoxic sites that generate N2 gas instead of the toxic H2S gas. That's why I was saying that if indeed this is the case in Ian's developed tank then it's good news.

I'm not sure it is though if he doesn't have porous rocks, deep sand, etc. Just wanted to ask...

 

[Darkmaverick]

Hi Tran,

I know you are not insinuating anything negative about anyone. I am complimenting that you mentioned a very good point and gave you rep points. There is nothing wrong with your post at all. I think you read too deeply into my feedback.

Its just highly unlikely for ianclick to be using deep sand substrates. You are right to clarify. It is good practice to ask to be sure though rather than make assumptions.

Well if he does use deep sand substrates, i guess he can find out by stirring the sand, releasing the gases and inhaling deeply. Anything reminding of rotten eggs or flatulence would indicate the sulphuric version.

Cheers.

 

[ianclick]

Hi all,

Thanks for the replies. No sand or porous rocks but .... ph in good tank 6.8 and in the tank with dropping nitrates 5.8. I didn't think about the pH at all so many thanks and I will see about getting the pH abit more alkaline and closer to neutral.

Many thanks once again it was driving me mad. I will post new readings in a week or so.

 

[ianclick]

I've just been in touch with our local council who tell me that they made some adjustments in our water treatment plant that may have caused the pH level to drop when I did the last water change although they wouldn't tell me exactly what those changes were.

However I have just tested the tap water and its 7 pH so seems to be back to normal.

Tank test 6.8 pH