Desperate for help, established tank dying

[Subsea]

Subsea", have not ever had a calcium reactor on this tank. Thanks for the link to the article.

My 25 year old tank was tied into a 1500G system which was maintained with calcium reactor. Mixed garden reef with ornamental macros, softies, lps, flame scallops, sea apples and numerous tube Anemone and various other filter feeders. I ran everything in manual. The metering valve for co2 required tweaking once a week as did affluent drip rate. For control parameter, I choose to use calcium. The test was easier for me. Also, because of fluctuations from coral uptake of alkalinity during photosynthesis, alkalinity measurements varied dramatically during the day.

 

[MarkW64]

I have replaced my rodi filters every 10 months or when TDS meter shows 5-10.

The one thing I would recommend that hasn't already been mentioned is changing your DI resin more often. I never let mine get close to 5-10. I usually replace when TDS goes from 0 to 1 -- I never let it get to 2. I know some people do OK with higher TDS -- it all depends what those dissolved solids actually are -- but you are clearly not "doing OK".

Good luck!