High DKh

Hey all not sure what the cause of the high readings are. the system is a
75 reef with a 30 gal sump. I stopped dosing B-Ionic which was the only
additive I add to the tank. I also have done two 30 gallon water changes in
the past 3 days to see if I can get the readings down. the reason for
concern to me is not any of the tank inhabitance but the fact that coralline
growth is very slow in this tank compared to my other tanks.

testing was completed with a new Salifert test (took almost the entire 1ml
to change the color) lfs gets the same readings. other tanks are reading
fine.

the specs are as follows:

SG = 1.026
PH = 8.2-8.3
CA = 420
DKh = 15
NO2 = Undetectable
NO3 = 2.5
Ammonia = Undetectable
PO4 = Undetectable

the tank is coming on 2 years setup, converted to reef 3 months back
(upgraded lighting and skimmer) has 150+ lbs LR, UGF filter w/ 5" CC
substrate (hey its been working for 2 years with no problems and I'm sure
its not the cause of a high DKh..........at least I wouldn't think so.)
lighting is 2 x 400w 20,000K MH on 12 hrs, return pump is Via Aqua 3600
estimated at 900 gph the UGF is powered by 2 Hagen 802 power heads, skimmer
is a very dissappointing Aqua-C Urchin Pro w/ Mag 3......thanks Marc its
been almost 2 months and it might be starting to "work out the kinks" but
its still not what I'd call "up to snuff"

inhabitants consist of:

2 Trachyphyllia Brains
2 Wellspphyllia Brains
1 Short Tentacle Fungia Plate
1 med size Trumpet Leather
3 sm to med size Toadstool Mushroom Leathers
1 lg Torch Coral (25+ heads)
1 med size Cabbage Leather
8+ 2"-3" Florida Ricordia
3 sm Blue Spotted Shrooms
15+ 3" Rodactus Shrooms
1 med Cauliflower Colt
1 lg Achilles Tang
1 lg Purple Tang
1 lg Yellow Tang (lets keep to the question at hand, no need to comment on
the tangs please i hear this enough over on RC)
1 Blue Devil Damsel
1 Three Striped Damsel
2 Reticulated Damsel
1 Mandarin Goby
1 HUGE Green Carpet Anemone (16+" when expanded and about 12" tall)
3 Porcelain Anemone Crabs
2 Giant Turbo Snails
3 Yellow Reef Chromes
6 Peppermint Shrimp
1 Derasa Clam 3"
2 Gold Maxima Clams 2"
Assorted Zoo's
100 or so Blue Leg and Scarlet Reef Hermits
50 or so Turbo Snails.

and todays count 2 damn aptasia's


Yes I know some of you are thinking I got a hell-of-a bio-load but it works
for me so please refrain from flaming and lets keep it to helpful advice
please.

thanks in advance

kc