Established Tank - Issues For A Long Time

Hi,
I was hoping I could get some input or advice a problem I’ve had for a long time now. Basically, I’ve had a tank (180 ltr) for over 5 years now and unfortunately I don’t have many fish in there as fish I’ve added such as Rams, Cardinal Tetras, Pygmy Corys and a few others have not survived. I do have Harlequin Rasboras and Flying Foxes which have been fine in there. Obviously throughout all of this time I have continually tested the water and taken many samples to different pet shops and ‘experts’ who have all been equally stumped and advised everything in the water tests are absolutely fine, encouraging me to add more fish, which is something I’m not willing to do until I find some sort of solution to this problem.

Water is as follows:
PH 7.1 (will sometimes drop a little of an evening when the lights go off) – the only concern I had with this is the tap water is more 6.8 or 6.9 but something in the tank has taken this up but then always stays a steady 7.1
Gravel all tested fine – I have in the past replaced this just to ensure that’s not the problem
Amonia – 0ppm
Nitrite – 0ppm
Nitrate – 5.0ppm

I’m close to giving up to be honest as no one has figured out what this is. My only conclusion is that it’s the actual tank because I’m completely stumped. I appreciate this is not easy to diagnose over text but if anyone has anything to add that’d be great and much appreciated.

Thanks

Thanks for your reply. I do have plants but they hardly flourish in the tank. I'm currently adding a number of fertilising products in an attempt to encourage more growth with them.

Do you have very hard water? I know it is unlikely with your pH but I need to check 

As for the pH, the tap water pH - is that freshly run or water that has been allowed to stand overnight? It is common for the pH to go up slightly in tap water that has been allowed to stand due to carbon dioxide gassing out (carbon dioxide dissolves to make a weak acid which pushes the pH down a bit. When it gasses off the pH rises).


I can vouch for java fern, anubias and bolbitis growing well on wood - or any other decor you may have in the tank. I cannot grow plants that are rooted in the substrate but those that grow attached to decor grow well for me. I just use Seachem Flourish (with nothing else in the name) as fertiliser.

Hi Lee, what is your water change regime?

How much water do you change?

Your low nitrate does suggest your water change regime is OK, though I need to check about the tester you use. Is it a strip or a liquid one? And if it is a liquid one, the instructions will tell you to shake one of the bottles before using it - do you shake it according to the instructions, or even better, more than they say?

Sorry to read about this. Not sure that there's anything I can add but I just wanted to check if this has been the situation throughout the 5 years? I'm guessing it has been but thought best to check in case the tank had been fine for the first few years but then the situation changed.

Moss balls are also good in the tank - I have a few and, apart from one which I think rolled up against the heater and is slightly discoloured in one place, they seem to be indestructible. I wonder if it might be worth giving something like a catappa leaf a try too?

Have you tested your water hardness as @Sue has suggested?

Your very soft water ought to favour the fish you've had. However, it may be that you should increase it a little so that there is some KH. If you can get some Tufa/limestone rock pieces, it may bring your KH up to 2. I keep some in my tank.

The lava rock won't help unfortunately as it contains no calcium carbonate which is what will raise your hardness.  This is the same thing that causes limescale on your kettle/taps.  This will stabilise the pH of your aquarium and aid the fishes bodily regulation.

Alternative would be to use a SeaChem buffer as per this useful article (http://kh-aquarium.blogspot.co.uk) which also explains why it is important for fish health:

increase resistance to degenerate diseases by lowering the acidity in the body. This will help with prevention of ich, fungus, and general “wear and tear” in your fish. Calcium also helps in healing and stress, and without proper calcium levels healing may be difficult or impossible.

It's a 180ltr tank and I change about 30ltrs each time.

I have 180 litre tank and I change somewhere between 60 and 80 litres a week.

Your very low KH would be expected to cause a pH crash as you are doing such small water changes - I have KH 3 and I need to do water changes of at 30% to stop my pH crashing - that has happened to me when I didn't change enough water.


With such a low KH I assume you also have low GH, which is the important one for fish, though the fish species you names all like soft water so they should be fine.