Pilis Nemzeti Park Fella

We've got a plunge pool in the garden, it's 8m x 5m x 1.4m, though it got a slow leak at about 1.2m so we only fill it to that level. Also the kids bounce out the water if it's full to the brim, they do a lot of bombing etc. It's all built above ground. It used to have a working filtration system but I messed up winter storage a few years ago and the ice expansion cracked the filtration pipes so we don't use that any more (as the water pours out), not that it was ever brilliant at filtering. So now we have a closed tank of water, well, open to the sun - we filter it by hand with 2 fine mesh sieves and that works pretty well, you can get most of the solid detritus out quite easily. Bit of an oily sheen from the suncream but no big deal. I've taken to shaving from a bowl with hot water from the kettle then skinny dipping in the pool for my morning shower (in the absence of kids!) - I also get the kids to jump in daily for their shower. No need to turn on the hot water, saves money. Garden hedges are thick enough to preserve my modesty but if some neighbour saw my bony ass, I'm not bothered.

We keep the algae at bay with a Multifuncios TablettaHUF 2290 for 1kg from Bauhaus or elsewhere. Not too bad, we need 2kg to last 6 weeks without changing the water - or else the deadly algae come & colonise really quickly.

Anybody got a cheaper/ more effective solution to algae/ general pool water brightness?