What is this product called here

Perhaps it would be better if you told peeps what you need it for?

its for doing this

Floor screed cement should suffice but a bit expensive at 10GBP just to mix a small amount.

The bag you show is ABS Flooring compound made by Optiroc. It us used as a self smoothing cementitiuos screed for floors. Optiroc do have a presence in the UK but only sell to the trade.

There are many similar products available in the UK but only through specialist builders merchants such as BBM.

It probably would be but might contain contaminants. There is a contact link on the home page.

With silicones the preservatives in industrial stuf might be enough to kill pet fish but I doubt cement would do as much if it were left long enough to grow algae. But why not try tile cement? The waterproof stuff should do.

Which product? and what home page?

Further to my earlier posting. Make sure the product has a DWI (Drinking Water Inspectorate) Approval. It is then safe for potable water and most probably Tropical Fish water.

Whatever you decide to use, it's very important to check on possible chemical leaching into the water. Cichlids and marine species are very sensitive to this as I guess you know.

If you can find the manufacturer web site, you can usually find the material safety data sheet.

Right. Plaster of Paris will do.

You can buy suitable pigments at the same place - an art or craft shop normally.

Will plaster of paris not dissolve in water after a period of time. I believe this is what those awful food blocks that you put in your tank when you go on holiday are made of, and they are meant to dissolve

Anyway, thats why its all post varnished.