This sounds like a fungal or bacterial infection and needs sorting asap as may infect the fish. You could take pictures of the spots and ask at the fish shop/pets at home what to get. Think they will recommend a water treatment but you may need to remove the fish.
They also advise a complete water change and to disinfect everything. If you do this it will upset the nitrogen levels etc so the tank with the fresh water in it should be left for 24hours and just add two fish to start with and introduce the others bit by bit.
any snails in the tank? they breed like made and create this effect or it could be a colonial bacteria, or excess food decaying I would suggest not disinfecting, you will lose all your bacteria and have to start from scratch, upload a picture and we can then assist,
how long has it been running? how soon after setup did the fish go in? tank size and filtration? number and type of livestock? amount feed?
Ok its been up and running for around 7 years (we bought house and owners left for us)
It has catfish type fish (plecto something) and around 10 community fish. Theres an apple snail and also some assasin snails,but have also noticed there seems to be lots of other snails that seem to have multiplied a bit. Got a trap thing that we are emptying daily.
There is a feed of granules once a day, plus an algae tablet for the catfish, though have been told to reduce it to once every 2/3 days if algae gets too much.
Light is on max 4/5 hours per day
Cant upload photos but does seem like photos of snail eggs now that i have googled that.
Any advice to get rid ? Or advice in general as very new to this!!
the assassin will run out of food eventually and die out, the apple snail will be a target before picking off each other.
the 2p sized wafers? yes on a tank that size unless over filtered and understocked maybe 3 a week tops, its not like the fish are having to work for food, so they will grow and gain weight just fine
lights only important if you want to see the fish/ growing plants
they say there's a thing called the 7 year tank crash, when detritus in the sediment builds up, take things very slowly and try to avoid sudden changes of large water volumes or disturbing more than 20% of the gravel at a time, then leave alone for a few days before disturbing again as you get sulphides and other toxins lurking there and you can crash the system with a sudden exposure to elevated levels.