Hi so my fish and snails are all doing fine but just recently I have been having trouble keeping my butterfly plecs alive I have lost 4 in total within a month. I currently don't have any but I would like to get one for the 60 litre and one for the 180 litre. I am just wondering if any one has any tips. They were all in established tanks with fish, the tanks had algea in and I was feeding them wafers and plecostomus tablet, they would also have a nibble on the cucumber when I put it in for the fish. Was there something that I was doing wrong? I really like butterfly plecs but I don't want to get some more if they are just going to die again. One I know got trapped under an ornament and I didn't realise and that's how he died but I just don't know with the other three. Two of them were fairly new when they died and the other I had had for about three months. I just don't know if it was the weather, the fish or something I did wrong. If anyone can help me with this it would be very much appreciated. Thanks.

I'd highly suggest bristlenoses to keep with goldfish, provided that you keep the tank a bit warmer (say 22-26 degrees celsius). I don't think any plecos would actually die from being stuck under ornaments as they are really nimble and can get in/get out from anywhere.
I don't actually know that much about butterfly plecos though, but note that most plecos grow really big and need large tanks to stay happy and healthy!
I also second the driftwood that skwishee mentioned. Plecos rasp their teeth on the wood to get extra fiber and stay healthy.

Telescope goldfish shouldn't be kept with fantails or orandas that are much bigger, it's better to have it the other way around to be sure it will get its share of food. Try to keep the telescopes about the same size or bigger than the other tank occupants. Other than that, keep the water quality lovely

With the 60 and 180 litres, I know the 180 litre is going to be Merle and Flash's tank, but what's in the 60 again?

Butterfly pleco's are tropical fish they need the temperature to constantly be around 24/25 degrees celsius, I'm not sure why you would have been sold them for a cold water goldfish tank, when it wouldn't have been suitable conditions?

If they're in the cold water tank, then they can't be butterfly pleco's, they must be the hillstream loach, which is sometimes called the hong kong plec But they are loaches not pleco.

Here's some info about them, that might help you out;
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I know generally these little guys need high 02 and a decent flow rate within the tank, as they come from high current environments. Not sure on their compatibility with platys though?

Ah well that's good
Do you have air stones in both tanks for oxygen and a fast current? I'm not too sure how the platys would be, if you increased the current, but the single tailed's would possibly be okay with it. Although I have heard of them being kept with fancy goldfish, where the current is immensely high, but they managed okay because they had the option of sitting in the stream from the filter out take.

I've considered having hillstream loach myself, by keeping them with white cloud minnows, in a river manifold set-up, so there's a fast flow for them 

60L is about the smallest tank size for a small plec and/or loach they like the current from a powerhead...I've got 2 bristlenoses in my 90L and the only time I worry is when I actually see them !