Nitrate spike

Hi all,

I tested my water parameters recently and they were all fine. I tested them today and the nitrate seems to have spiked from what it was, about 5.0, all the way up to I'd say about 30ppm. Ammonia was a little on the high side too at 1.0.

I have run out of liquid for the nitrite test but I'm heading out to get some later on this afternoon.

I've done about a 60% water change and re-tested my parameters. The ammonia is now back to 0.25 and the nitrates are sitting between 5.0 and 10.0 (more towards the 5.0ppm though).

Any idea what could cause such a spike in a relatively short space of time? I do 1/3 water changes every week. I have one axie in the tank and he is healthy and eats well, so there are no issues with his health.

I've tested the PH there having done the larger water change and it's sitting at about 6.8.

I'm not hugely concerned by the nitrates being a little on the high side but wondered what could have caused this?

One thing I have noticed is that the duckweed in the tank seems to be growing at an alarming rate. It's so thick now it's starting to sink and I'm removing some of it as I don't want my axie getting tangled in it. I suspect this is probably linked to the nitrate spike but would appreciate the advice of the more experience members!

Should I be concerned? There's no algae growth on the sides of the tank or anywhere else that I can see. Also, tank water temp has been 18 degrees C so perhaps the warmer temp has stimulated the duckweed growth and caused the spike?

I should add that in the afternoon, the sun is directly on the tank. To combat this, I close the blind on the window and also have a cover that I place over the side of the tank that the sun hits directly. The interior of the tank is much darker when I do this so my axie isn't uncomfortable (also keeps the water from heating up) but now that I think about it, maybe the duckweed is getting enough sun to grow?

Sounds like your cycle isn't quite there yet - how long has your tank been set up?

Nitrates are the end of the nitrogen cycle and can only be removed by water changes or absorption by plants - if you have a spike it's usually a missed water change or something left in the tank slowly decaying.
The duckweed is feeding on the nitrates and sunshine, hence the growth rate - just chuck out any excess (or sell it on eBay!) and let it do it's own thing.

The tank's been set up for almost a year now, very odd.

When we got the axolotl the man who raised him gave us a sponge for the filter that had been "seeded" (his words, I didn't know what he meant at the time!) from the tank the axie was brought from and the tank was allowed to cycle prior to the axie going into it. My husband did that as it was his colleague who gave us the axie with all the instructions on setting up the tank.

The only thing I can think that might have happened was my husband did the second last water change and when I asked him if he'd rinse out the sponge he said he'd forgotten but would do it. I suspect he didn't get around to it. I did the water change about four days ago and rinsed the sponge out (with tank water) so maybe the nitrate spike is a by-product of him not rinsing the sponge though the week before.

There's no old food in the tank, my axie gobbles up everything that comes near him, including attempting to eat the thermometer whenever he passes it.

Hmmm... Thanks anyway. Spouse shall be suitably punished with a stack or ironing or similar

What anti-chlorine do you use?

I normally use Nutrafin Aqua Plus, but a few weeks ago I ran out and needed to do a water change before my new order of it had arrived. I bought Aquarian Goldfish water conditioner from Tesco (all my LFS were shut!), and the day after my normal 20-30% water change using the Aquarian stuff I had spikes in ammonia and nitrate.

I got them back down with a 20L change every day for a week, but it's never happened before. I would warn anyone off using 'cheaper' dechlorinators now!

I've got API tap water conditioner from Pets at Home. I can't remember if it was cheap but my test kits are the same brand.

If you have ammonia and nitrIte in your tank, then im afraid it isnt cycled
Even when doing a fish in cycle you shouldnt let the ammonia get above 0.5ppm.

NitrAte is okay up to 40ppm so i wouldnt worry too much about that but you need to start doing daily water changes of around 10-30% to keep the ammonia below 0.5ppm, then when your tank stops showing readings of ammonia and nitrIte, switch to once weekly 30% changes

Thanks everyone. I tested my nitrITE and it's sitting at 0.

Very odd, I guess Mr Fireball not cleaning the sponge has somehow crashed the cycle. To make it up to my axie, I bought him a floating football when I bought more nitrite test liquid.

Ok guys we're now at PH 6.8., nitrite 0, ammonia pretty much 0 (a lot less than 0.25 now) and nitrate I'd say just over 5ppm.

The tank was cycled prior to this as my readings were fine. I know that higher nitrates can occur at the second cycling stage but we had the cycle established. Something has obviously crashed it and it's bugging me.

Hmmm fixed now, and i have a lotl who is gazing at his new toy like it's a spaceship!

Thanks for the suggestions and help


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