albartsch, The obvious question is coming; how long have you had your pond? I've seen people mentioned here and else where that a pond takes a year or more to mature. My pond has gone through three clear / green/ brown / clear cycles since I started it up in October. Sometimes it just takes time, and patience. Allow for the beneficial bacteria to catch up. Don't feed your fish for awhile, clean out any floating debris on your pond surface, check to see that your UV is working right (Not burnt out -UV loses a lot of its effectiveness when it runs through a heavy green sheet), and make sure your filters are free of build-up. And one day, you'll come out and BAM; it's clear. LP

I'm not sure what you want to do. Do you want to dig a second pond next to what you have now, cut away some of the preformed liner to connect them and then glue the EPDM liner to the preformed? That has little chance of working. But if that is your plan, just get an EPDM liner big enough to line your preformed and the new addition.

The easiest way would be to use bigger yarn and needles. Can't tell you how much that will enlarge, though. For example, I have a pattern for a reindeer that calls for dk weight yarn and size 3 needles. The reindeer was supposed to be about 8 inches tall. I used worsted weight and size 8 needles and he stands about 24 inches tall.

Let me say from the outset shelves provide easy access to your friendly heron and maybe even assist mink if you are cursed by their presence. I have had a heron stood on the plants/plant-pots on my 2ft deep shelf and at 70cm deep your pond will, most likely, not be heron proof. My fish pond has a 4ft deep section that, I think, saved my fish form the heron. That said I wouldnt be with out shelves, you pays your money and takes your choice. Assuming by straight Alan means vertical I would ammend his last paragraph to read " .....straight sides are good, IF THE SOIL WILL TOLERATE THEM, as long as......". With regard to shelves, what sort of plants are you thinking of and is the pond to be wildlife friendly, if the latter then I would suggest additional shallower shelves. Shallow shelves especially with a low surround help any animals that fall into the pond escape and very shallow shelves are baby amphibian friendly. My shallowest shelves, in ponds 2 and 3, a wildlife pond and a plant pond, are between 1" and 3" to the liner. In the wildlife pond the plants are planted pot free in garden soil. Some of this soil broke the surface but last autumn I did a bit of tinkering which deepened the pond by an inch so I may have to add some gravel to get back the through-the-surface shelves. Garden soil may have been a mistake as it adds nutrients to the water and feeds blanket weed. Last autumn in an attempt to reduce blanket weed in my fish pond I reworked the 1ft shelf so that the plants are pot free in gravel beds. The idea is that the soilless planting will cause the plants to draw nutrients from the water, thereby combating blanket weed. I think Sue, Scotty, does this. I am going potless because I hate ripping roots off plants in order to repot them. Going potless I hope not to have to lift them at all. The MAJOR drawback with this is that over time I expect everything to grow together and my gravel beds to become 'one'. If this doesnt suit dont consider potless planting. If you do consider potless planting to be a possiblity it would be an idea to 'lip' your shelves with raised edges as these will help retain the 'media' on the shelves. However be aware of plants with sharp roots or that spread by runners. I have yellow flag iris contained in a soild wall pot in the fish pond and will be lifting some of the reeds and rushes in the wildlfie pond and putting them in solid walled pots too. Soild walled pots = cut down washing up basins etc. With regard to the depth I would try to go deeper than 70cm if you can, heron protection. A shelf or area at 60cm is not a bad idea for lilies, water hawthorn and maybe even golden club. The more vigourous lilies can grow in water deeper than 2ft but hawthorn and the like would probably struggle. Hornwort will grow in any deep depth as will most of the planted oxygenators