I have a problem with nitrates keep jumping up, the tank is about a year old and had no problems until Christmas. I always did weekly water changes of 30-50% depending on test results. Just before Christmas I purchased a couple of swordtails, and both died, along with a tetra within 3 days of each other, they had been in the tank less than a week. Alarm bells rang, I tested the water and the nitrates and nitrites were higher than what is considered normal (I can't remember the exact read outs now). I went online and everything seemed to point towards old tank syndrome, I started doing daily water changes of two buckets, that is about ⅕ of the tank capacity. I did that for nearly two weeks, then decided it wasn't getting me anywhere. At the weekend I did a 50% change on Saturday and a 50% change on Sunday. The test results looked more promising, but I tested again the next day and they had jumped up again.
I use Tetra 6 in 1 strips.
Results on 20th Jan:
Nitrate 39 mg/l
Nitrite 0.05 mg/l
Carbonote hardness 16
Results on 21st Jan:
Nitrate 60 mg/l
Nitrite 0.18 mg/l
Carbonote hardness 18
I use the Tetra app to get the readings rather than relying on my eyesight. I use the API ammonia test and find it hard to read, but it always seems to be fairly yellow, (0.00 - 0.25) and if I am in any doubt I use ammonia remover.
There has been a lot of algae on the glass, which I scrape off. I have been putting this down to the nitrates/nitrites.
I'm not sure if it is old tank syndrome, whether I need to buy a new filter, or if it is due to overfeeding… I feed every other day, some aquarian tropical flakes and 1 algae wafer for the pleco and the corys. I got the pleco in Nov, it doesn't seem to touch the wafer much, the other fish seem to peck at it. Today I removed it after half an hour it in case the rest of them were eating too much.
I need to buy some more real plants, I took out the ones I had as they were old and dying.
Other things you might need to know:
Tank is 112 litre Aquael
Filter is Aquael fan 2, 1 year old. I use Juwel filter media cutting the various sponges to size and stacking them like in a Juwel filter (I used to have a Juwel tank years ago and liked the filter media)
UV attached to the filter
Temp is between 75 and 80 fahrenheit
Halved coconut for shelter, which was boiled many, many times before putting it in the tank.
When your tank is in "old tank syndrome" it's not cycling any ammonia but the process restarts after the water changes. When that happens, all the accumulated ammonia is processed into nitrite and then nitrate so you will see a big jump in nitrate.
Keep up daily water changes whilst you have any ammonia or nitrite in the tank as they are quite toxic to fish.
Nitrate is the end product of the cycle and as such can only be reduced by regular (at least weekly) partial water changes. These changes will also prevent another episode of "old tank syndrome".
There is often some nitrate in the tap water in the UK, so your tank level will never be lower than that. Test your supply and then aim to maintain the tank at no more than 20ppm above the level in the supply by changing enough water every week to keep it stable at that level.
One other point strikes me. When you say "I use Juwel filter media cutting the various sponges to size and stacking them like in a Juwel filter", do you mean that you're regularly removing and replacing the filter media?
Filter media should simply be squeezed/jiggled in being-removed tank water during a water change, rather than replaced. However, if it's absolutely falling apart, then it can be replaced - just a little bit per water change, though.
If you're gently squeezing/jiggling the filter media, or replacing it in small quantities at a time, then there's no cause for concern in that respect - just ignore this post. However, if you are removing and replacing it in its entirety, or did this around Christmas just before the problems started, then it might be that the filter has been going through a new cycle (as well as having to cope with the extra bioload from the new fish). If that is the case, then this https://www.fishkeeping.co.uk/articles ... ammonia-nitrite-spike.htm might be helpful.