DIY Sump Design - HELP!!

I have been running a 'Ratz' Trickle Filter/Sump system for 12 months and am
unhappy with performance. It is a 100 gallon tank with 60kg of Living Rock
running for 10 months now. Low stocking density but I still struggle to
control hair algae and water quality will not support an anemone (lost 4 to
date) but all else surviving ok. PH=8.2-8.4, Ammonia=0, Nitrite=0,
Nitrate=5-10mg/l, Phos=0, KH=8-12, CA=420-450, Mg=1250-1350, Salinity=37ppt,
Temp=26-28DegC

I think my flow rates are low and nitrates are hard to control. I like the
idea of a refugium area in the sump to grow some caulpera under 24 hour
lighting. Don't know whether I should use a DSB or try using 'Miracle Mud'
... any comments/suggestions would be appreciated as I want to get it right
this time!

I was planning to buy the glass and fabricate my own sump with a refugium.
Would like to also increase flow rate to/from tank from current 2000 l/hr to
around 3500 l/hr.

Can you point me in the direction of any good sump design data - Eg Flow
Rates over Refugium section, Wier Heights, Use of Combs, microbubble
elimination, light mounting, etc. There must be some best practice
guidelines somewhere .. I can't find any that I could depend on!

Could also do with some tips on plumbing for the best flow. Is it viable to
use 2 smaller pumps to feed the tank? (in case one fails when I'm out). My
tank is 5ft long with 20" of width available under the stand - hopefully
plenty of room. Is it a case of the bigger the sump the better?

John C