Anti-Social Fish

Question
I have a biorb 35l tank and have 3 goldfish 2 comet and 1 blackmoor. The fish have been very happy for the time we have had them (which is only a few months)  
The biosphere has a filtration system. I cycle 25% of the water every Sunday and give the tank a general wipe down of algae on the sides. Every 3/4 weeks i give the bottom a bit of a suck but thats only when i change the filter.  
We feed them a mix of flakes and sinking pellets once a day. Once a week I feed them chopped fresh peas or cucumber.  
Yesterday we changed the light in the tank from a halogen light unit which we switched on and off, manually, to a LED Intelligent light unit that has a 24 cycle of moonlight and daylight.  
I don't know if it is a coincidence or if it is a factor but since the new light has gone in the fish have become very sedate lying on the bottom of the tank and hiding behind the greenery that we have in the tank.  
My fish have always been described as happy fish but at the moment they are not looking so happy. They have become very anti-social.
I have visually checked that they do not have any black spots on any of the fns of the comets and there does not seem to be any bloating but i can never tell really due to the contours of the tank.    

Please can you help?

Answer
Hi Helen;

It may be just a coincidence. You might check the levels of ammonia and nitrite. When fish are lethargic or hiding more than usual it can indicate low oxygen levels and possibly elevated toxins such as ammonia and nitrite. If your fish have grown since you've had them they are now finally getting too large for their tank. Goldfish are very messy guys that need at least 40 liters (about 10 gallons) just for one fish. As they grow it just gets harder and harder for the filter to keep up with their wastes. Here is a web page about their care and what they need;

http://www.firsttankguide.net/goldfish.php

In the meantime, make a 25% water change every day until they seem to feel better. All tanks need a weekly 25% change with a gravel vac anyway. I hope they do okay...

At Your Service;
Chris Robbins