Have a bi-ube thing, which is rubbish IMO, but found a snail in there off one of the plants we bought.
Then noticed a couple more snails.
Yesterday noticed water was very cloudy, even after cleaning tank and replacing the crappy filters you get in these things about two weeks ago, and this morning, the black fish we've had for three years was floating at the bottom and the other redcap fish (we've only got two) was struggling to swim. Emptying the tank, I found about 20 snails and those transparent egg things covering almost every rock.

Did these kill the fish, there was an excessive amount of eggs and snails in there.

theres no chance the snails would cause death to the fish
and snails are bivalves which makes them a natural filter so they would not have caused the water quality to deteriorate

when you clean the filter make sure you use tank water not tap water

if as you say you have recently added new filter media then its likely by removing the old media you have created a situation whereby the new filter has no beneficial bacteria existing to control the fish waste. Therefore the water clouds as ammonia and nitrite start to build up in the water.

the best option is to do small water changes each day and make sure you use a tap dechlorinator to remove the unwanted chemicals in our drinking water

Some tanks take a long time to settle and can be unstable. We stopped getting shrimps because everytime we used them , the tank would cloud up a couple of days later and take a week to settle down again.

Biggest problem is usually overfeeding but its difficult to stop kids shoving food in.

Never clean your filters in tap water hot or cold because it kills off the bacteria you've carefully grown on your filter media which help keep your tank clean. Rinse the parts and sponges in the water you've siphoned off when you do water changes. Also i hate snails,even when you don't want any they appear after a while. I always take them out and dispose of them, else you end up with hundreds of the beggers.

bi-orb are good for a few neons or shrimp maybe. I'm guessing from your description that your fish are a redcap oranda and a black moor goldfish. These might grown too big for a biorb and a tank might be a better thing.

sounds like poor water quality,dont take all the water out of your tank just empty 20% water, and do a water change evry 2weeks,Giv your plants a gd wash before putting them in the tank Aswell,

Has some one been over feeding them, the cheep fishfood makes water cloudy, wilkinsons is the worst fish food to buy...

I used to change my water by one bucketful each week. If the bucket is left standing overnight the chlorine comes off it and it also comes up to temperature. Take a bucket full out with a siphon and then replace it with the standing bucketfull. Worked for me for years. Cloudiness caused by over feeding, my grand daughter does the same in spite of being told not to. Just put enough food in for them to eat in a couple of minutes and just once a day. Realise may be trying to teach my granny to suck eggs but just in case.

The problem with modern water supplies, is the water companies are increasingly using Chloramine instead of the more costly Chlorine to make the water safe, and that does not disappear naturally, it can only be removed using a man-made agent.

Ive never had a problem with cloudiness in all my years of owning a tank, so I dunno if as jase says, its more down to the quality of the food; I don't overfeed by choice, but im sure I must do sometimes. I do however insist on using known brands like Tetra, im currently using King British and Aqua One Spirulina and PetsAtHome plec algae pellets as the staple food supply (with variation in fresh vegetables etc), and never had a problem.

My mum on the other hand uses the cheapo food you buy in the likes of Home Bargains, and she does sometimes have issues with cloudyness. The filter she is using is more than big enough for the tank, so it could well be the food.

I have a Rio 400 with is around 450 litres, and a Rena XP4 filtration system, suitible for around 600 litres iirc, but it can't be tank size as I used to have a 30 litre tank, with 3 goldies in (babies) and that never got cloudy either. Actually, at present, im running an unfiltered 25 litre tank, with baby swordtails in, and that too doesnt get cloudy, do its nout to do with filtration or size.

As people have said, when getting plants, always wash them first with some water out of the tank, as snail eggs tend to enter the tank via plants, and if they have come out of bad water, they could potentially infest your tank with unwanted/harmful bacteria. The same applies to the filters, when washing them, just use water out of the tank, and dont squeeze etc, too hard, as you don't want to damage the biological filtration element, which is the most important element in a properly cycled tank.