you dont list your s.g.....hopefully 1.023 to 1.025...also check ph at night,,and at day is it at 8.00 + at night and 8.3 to 8.5 in the day?? are u running good carbon??? mushrooms and zoes are chemical demons at times and all that in a 40 needs carbon or reg waterchanges,,like 10 gallons every 2 weeks or so. What salt u use? do you mix salt atleast overnight? algae is feeding on something,,either nitrate,silicate,or phos. when checking for these,,use water from around substrate that been just a little disturbed,,also nitrate test kits are not reliable as they should be..check results againt diffrent test. hope any of this helps