Discus, carbonated hardness, buffering & plants

Hi guys. Have had issues with algae and my largest discus (he's eating fine, behaving fine but looks blotchy as per prior posts and pics. At same time I've been fighting and losing a battle with beard algae. Two questions:1. aquadur buffering agent to rise kH and discus keeping and 2. Strategy to minimize algal growth while maximizing plant growth

Tank parameters:
Ammonia and nitrites 0
nitrates at 5ppm (or less).
Phosphates at 0.5ppm so no issues with nutrients per se.
GH at 2 and KH at 0! Strange to have no buffering capacity in an established tank but such must be the water supply.
PH at 6.3, tank at 28c
2x54watt t5s and 4 TMC aquagro aqubeam 600 ultimasfor 9 hours per day - just reduced this to 8 hours.
Co2 on 1 hour before lights and off 1 hour before they go out.
Uv sterilizer on from lights out until 11am (12 hours).
375litre tank.

1. Having no buffering capacity is obviously dangerous when it comes to pH fluctuations. Anyone use jbl aquadur plus to buffer water for discus?
2. Am I using too much light for plants given tank size and hence getting algae too. These tmc aquagro aqua beams are supposed to be optimized in terms of the light spectrum but the old watts per gallon doesn't apply when using them...

Had a good chat with Darren at SH today and going to increase amount of c02 from the 20ppm currently. I've never used a buffering agent and just a little cautious about it.

Advice appreciated as ever....

Thanks!

Brian

From my experience with planted tank i'd say phosphates and nitrates at any concentration + loads of light = algae
Registering those two means that there is still some unused excess which end as algae food
I would plant some fast growing real water plants like vallisneria gigantea or hygrophila polysperma, they should mop up what's there

That's just it Bart, I don't have any excess for them to mop up. I've a 10:1 ratio of nitrates to phosphates which Darren was telling me today is ideal....I will however plant some more fast growing plants....I'm just sick of having to rip up plants covered in algae.....driving me mad! Cheers...