Feel like a newbie again.

[sugarplumfairy28]

9 years we bought 3 fish, all goldfish. At the time we bought everything we followed every piece of advice given, the filter, the food and the size of the tank, but I'll be honest I have forgotten what we were told at the time, with regards to fish size/quantity/tank size. We also added a little pleco to the tank which we were told was fine.

We emigrated and bought the fish with us! Unfortunately around 3 years ago we lost 2 fish and the pleco due some issue with a water change and the wrong chemicals given by the fish shop. We were left with a single goldfish in our upgraded 150 liter tank. (The filter and pump are specific to the tank but to be honest I couldn't tell you what they are) only that we were told this arrangement. We got Baldrick (yes that's the fishes name) a friend to keep him company.

There is no heater in the tank but there never has been either, and we were told that was fine for the pleco and the fish we had.

So we have a 9 year old fish who is approx 10cm, and a newer goldfish (Bingo) who is approx 8cm. We would like to add a Pleco to the tank but I can't find any clear guidelines as whether it is possible, even though in essence we have less fish and a bigger tank now.

The fact we have a 9 year old fish would suggest we're not doing a bad job! But I'd like to sure of what we're doing. Any ideas?

Sounds like you're doing well at the moment.

Personally, I would not add a pleco. While some species are hardy, they are tropical fish and some species can grow very large. They're also known for developing a taste for tank mate's slime coats - basically sucking on the side of slower fish and that would definitely include large Goldfish. On top of that, they are really heavy waste producers so will be an added strain to your filtration system.