Platy faeces problem

[Idris]

One of my two (m) platties frequently trails a long strand (an inch or more) of faeces from his vent.
Usually it is immediately after eating but in the last few days it seems to be independant of feeding.
Initially it was a similar colour to the food flakes (mostly pink/green) with some white and it usually got to about an inch long before he usually shook it off.

Last night the strand was about 3" long, thicker and black. He also was hiding in a cave, which he's never even seemed to investigate before. Eventually in an effort to find him I managed to spook him, at which point the strand detached and he seemed happier.

From what I've read it doesn't sound quite like HITH or constapation (although I can't really say whether he looks particularly bloated).

Any ideas what's causing it?
Do I need to worry about it?
If so, what should I do and how urgent is it?

Tank = 30L
3 1/2 weeks old ... 2 1/2 with fish
(Didn't get a chance to fishless cycle as I couldn't find any ammonia.)
Ammonia = 0.25
Nitrite = 1.6
Nitrate = 50
pH = 8.5
dH = I don't know, but from the amount of scale we get in the kettle I'd say it's quite hard.
Plants not doing particularly well.
Some algae developing in the last week.
One snail seen and removed today.
Feeding with flakes twice a day.

 

[Rodders]

Couple of my fish still do it now and my tanks just coming up to a year old. They've never suffered from it from what I can see. A more varied diet helps, some bloodworm, shelled peas and flake.

I also wouldnt feed then twice a day on a 2 1/2 week old tank as the ammonia and nitrite levels will go higher than you want. I cut mine down to once a day and it really helps. You dont want any new tank syndrome.

As for algae, how long do you have your lights on for. I just changed my lighting cycle to include a few hours of lights out during the day and that really helped me. More than 12 hours is bad anyway. People say 5 on 2 off 5 on. Mines slightly different but still has the same effect.

How many plants do you have, whats the coverage like? You also should work out the watts per gallon (WPG) your lights are giving out for your tank. If you go into the Plants and Planted section theres a lot of info 'pinned' in there. Different plants require different light levels and also CO2 if lighting is above 2WPG.

 

[laurasmithuk]

what othe fish are in the tank? tour NitrItes are extremly high.... i have just had a mini cycle and my nitrItes went to 0.50 and that caused me a massive ammount of probs

 

[Idris]

No other fish - just two platies.

Is there anyway to get the nitrites down other than water changes? I did a 30% water change on Sat and the next morning the levels were the same. So I did it again on Sunday and 24hrs later it was just the same.