My alkalinity is running at 6.8 meq/L, calcium is 400 mg/L and pH is 8.3, nitrates are 20 ppm. Most of the clams on my live rock have died and the corals aren't as perky. I use the B-ionic 2 part additive. I've done 3 water changes in 3 weeks. What else can I do?
Are you sure it's the alkalinity that's killing the stuffs? 6.8 isn't as high as mine used to get. Not that it's a OK level, but it should be something else killing your corals.
What are other tank specs? Tank size? Lighting? How long has it been established? What's the source water for top off? What's the salinity? Ammonia? Nitrite? Is there any temperature swing? Have you used any medication lately?
"clams on the live rock died".....What kind of rock do you have? What kind of clam is it? Some ot the rock may not be coming from tropical region and those temperate clams will die anyway.
Other specs of the system are 125g tank with 440w VHO lighting, salinity is 1.024, tank established for 1.5 years and source water is "soft" water with additional 5 micron filter
Stop doing water changes until you have tested your new water to be certain that it's not raising your alk. When I test my NSW I get a reading of 7meq or more, doing water changes isn't going to help. The best thing to do is to wait it out, I lose about 1.5- 2meq per week if I don't add buffer to the tank. Also hold off on any other type of buffer until things settle down.
Has this been an on-going problem, or happened recently?
