BUTYL liners do NOT leach chlorine... but if you are in any doubt, get samples of liners from your local pool store, roll them up, in a glass of sea water for a couple of weeks, then use a pool test kit to test for chlorine. all PVC fittings can leach chlorine, but the levels are negligable. I agree with Mike... a small(-ish) round pool would be the best option, but you should replace the PVC liner with Butyl. Back in the UK, we retro-ed a 15' round pool with a full-size surface skimmer, sand filter and 1HP pump! The angled outlet was pointing away from (but mounted right next to) the skimmer, and resulted in the whole pool turning into a giant vortex chamber! the pool accumilated all the debris in the centre, and the only clean it ever needed was to vacuum an area about 2' round!
If you mounted a bottom drain in the centre leading out to a pond-style foam filter, you'd hardly have any maintenance (in the water) at all
If you went for a box-welded liner, you could request a pattered sand coloured base... I've seen liners with a sand and pebble design on them.
Use obscene amounts of UV, and use ozone in your skimmer, and you may even be able to keep the algae down!
How are you maintaining the temperature in this? have you thought about water-changes yet? look on Horticultural websites for 1000 litre (food grade!) opaque water storage vessels