hear algae + browning corals

[KevinK]

i have hear algae slowly messing things up + corals seem to get brown a bit

ok so I occasionally had a fluff of hear algae, once here, once there, nothing out of the ordinary

now the last, about 2 months, it seems to get out of control, and my frag tank is slowly starting to become a big mess. my tank sand on the bottom is 1/8 covered with fluffs of it, and along the overflow I can almost use a mower.

my corals are doing fine, however not that I feel like yes, I feel thy could definitely be better, colors are on the brownish side of som

my values are:
mag 1260
cal 430
ph 7.9 mornings and about 8.2 evening (calibrated)
KH 9
temp 79.6 (0.3 variation)

these numbers are almost 100% steady, maybe calcium some times 20 off ore so, but that's it

my phosphate is 0.00 (salifert test kit, as well as hanna checker), both tested with at least 2 different test !!
amonia = 0
nitrite = 0
nitrate = 0

all tested with new Salifert

my tank:
- 350 Gal main tank
- sump with about 50 gal water
-frag tank with about 50 gal (has a sand bed of about 6 to 8 inches)

- main tank has 3x 250W phounix + 1 LED unit
-frag tank has a 150W phounix

all MH are about 3 months old, and had the same before, I changed each week one bulb

water circulation:
- 7x hydor coralia – 4
- 2x maxi jet 1200 _ upgrade
- 1000 gph pump on sea swirl
- 1000 gph return from sump
- 1 hydro coralia 3 in frag tank

fish:3 tang’s
3 clown’s
2 fire fish
3 damsels

food:
own mix of frozen cubes of:
- Sea food mix,
- misty
- cyclop.

one small cube a day (split out over 3 to 4 times feeding

skimmer:
a DIY 65 inches tall 8inch tube with air pump pushing 2000 L/h

ad ons:
1 L np bio pellets

last 2 weeks I added carbon, now I have to say that I never used carbon, and recently started with a phosban reactor filled wit it (last 2 weeks)
as well as I found out that there was only about 700 ml of pellets left, so added another 1000 ml = 1700 ml (last week added)

water changes I have to admit, I’m always behind what I want to do, so average it is 25 gal each 6 weeks (want to do this amount each 2 weeks, but .... (no excuse)
what have I dun –

what changed:
well in fact not much, other than that I always feel that skimming could be better, but actually he is working gust fine I think (maybe I have this feeling because it is a DIY.

I have a new pomp ready for my skimmer, hoping I can put even more air in it, like 3000L/h,


any idea where the hear algae are coming from ??