Fish Dying Off In My Tank Over The Last 3 Months

HI
Not sure if this is the right section to post my query, so apologies if it is.

In the last 3 months my fish have been slowly dying off,   by about 30% .

I've removed some of the dead which I found at the bottom of the tank. None showed any signs of disease, none were seen gasping  for air or had buoyancy problems.

I checked at my local MA, yesterday, who suggested possible bacterial problems, thinking I might have be over keen  with cleaning the media even though I've been doing it the same way for about 5 years. Is there are likely/possible alternative cause?

Anyway this morning I cleaned  the filter media(it was due). Instead  of replacing the oldest layer of filter floss, which I would normally do, because there was VERY little debris (it's an oversized filter for my tank capacity). due to the lower amount of waste material I cleaned it instead and put it back in.

Did I do the right thing?
 
I also bought some Aqua balls, wanting to avoid a chemical route,  and put them in the tank  the second best location ( unfortunately I read the instructions about the best location for them being IN the filter AFTER sorting out the filter -and setting it up  again). Can add an extra couple of balls to 'make up' for the balls not being in the effective place? Or not?

Many many thanks

Rosie

PS Before I really started looking at how there was some clear reduction in my number I bought  5 Albino Corys , mid March lost 2, and then stupidly with hindsight,  bought another 5 more recently. So 10 in total. I now have 2 of them left.

Hi rosaleen

Can you talk us through how you clean your filter media? It should be done in old tank water or dechlorinated tap water to avoid killing the beneficial bugs.

Furthermore, you should never recommend place more than 2/3 of your media at one time and aqua balls definitely do need to bring in the filter to work.

Hope that helps, I'm sure that between the members of this forum, we can sort this out for you 

Hi
Thanks for all your posts I really appreciate it. I'll try to cover all your questions.
Firstly cories,  I should have said the first five were peppered cories, definitely bought mid March
The second lot of five, were albino cories bought mid April I THINK. Both lots were bought at the same place.
They were not the only ones I have lost.........
6 neons in December  went down         2 now
6. Red  phantom tetras in December     1 now
6 shrimps December                            3 now
5 copper harlequins December               2 now.
1 rabbit snail OK
1 Bristlenose OK
6 penguin tetras December                   4 now.
3 Rummy nose  tetras December.           0 now

Cleaning the filter. I slways use the  old tank water straight after I've done a water change.
I always test the water when I do a water change. And to check my parameters were right this time  I'd had  the water tested at the MA the day before I did the clean.. They used the strip tests which I'd never seen before. Some slight variation but nothing untoward.
Sorry your advice about 2/3 of the media I couldn't quite understand. Typo error?
In the filter  there are 3 layers of filter floss.  I normally replace  the oldest layer, the dirtiest, with new floss. But because of the possibility of insufficient bacteria, I didn't this time. There was very little dirt on it.
The two other floss  layers,  the 2 different sponges  and the bio ceramics are cleaned in the old tank water.
Thanks for the info on the aqua balls.,  interestingly I'd put them in an old net by the intake strainer  and they'd disappeared / dissolved by the next day.
The thing which might be a problem is the temperature. IF I have gleaned the right info(different sites recommend different temps) The rabbit snail "needs warm water" 27degree upwards and the cory "likes cooler water" below 26."
I hadn't checked this before. I got the cories. And it doesn't explain the other deaths.
Thanks again for  your help. I hope I've covered all the points you made.
Rosie
This doesn't explain the other deaths

Do you know the pH and hardness of your water?

The nitrate test - do you make sure you shake bottle #2 very well before using it, then shake the test tube for 1 minute before starting the 5 minute timer? Failure to shake bottle #2 is the most common cause of inaccurate nitrate readings. It contains a reagent that settles out to the bottom of the bottle. All that shaking is necessary to redissolve this reagent. In fact, most people shale the bottle even more than the instructions say.

If the nitrate reading does prove to be high, it is an indication that you have too many fish or you aren't doing enough/big enough water changes or you are overfeeding the fish. High nitrate also means that other things we can't test for (eg plant hormones) are also high.

I'd be slightly alarmed by the very high nitrate reading on the test-strip, in the sense that, using both liquid-based and paper-based test strips, I find the nitrate and nitrite readings very accurate on the strips, and tend to believe the nitrate one over the liquid-based testing kit - clearly, my arm isn't strong enough to do sufficient shaking required of the liquid-based test! For that reason, I'd definitely repeat that test, with plenty of shaking and banging, to try to get a more accurate reading. [I've never used a paper-based ammonia test, so can't comment on that.]

I'd also check your tap water rates, just to see what nitrate is coming out at - is it similar?

The best way to keep ammonia and nitrite at 0, and nitrates low, is frequent and larger water changes.

The best way to keep ammonia and nitrite at 0, and nitrates low, is frequent and larger water changes.

The best way to keep ammonia and nitrite at zero is to have a filter with a fast enough flow rate, and enough media, for the bioload on the tank. With a suitable filter there should never be measurable ammonia or nitrite.

Quote from: hampalong on June 13, 2016, 11:41:33 PM

With a suitable filter there should never be measurable ammonia or nitrite.

Very true, I wouldn't expect to find either in my established tanks. Rosaleen is a pretty new fish keeper so she's still learning her way and everybody expects hiccups. We just need to figure out exactly what caused her hiccup 

The ammonia, probably. That's why we need to know details of her filter.

As others have said, if your Ammonia is anything other than 0, that's a problem that needs addressing.

However, with a tank that's been running for 2 years or so, it may simply be a matter of you over-cleaning and inadvertantly removing some of your denitrifying bacteria.

Indeed. Are you cleaning your filter sponges in tank water (as you should) or are you cleaning them in tap water (which contains chlorine and will kill your denitrifying bacteria)?

Are you using a dechlorinator in your water change water?

Hello to, well everybody!
Slightly overwhelmed by all the queries I'll try and answer a few at a time if that Ok
Firstly Sue re nitrate testing I always do the appropriate shakings  and use a timer to make sure  i do them correctly and wait the five min.
I have had high nitrate before as I said ybut not now and the fish weren't dying off  then. I'm not convinced with the strip. I I will do an API test later today.
 I did buy a JBL easy test when I was at the MA but don't know which letters mean what,  if you see what I mean so haven't used it yet.
Will answer more queries later, sorry, busy morning
Rosie