Can you retest your Nitrate, Nitrite and NH3 levels for us? At 9 months of running unless you have somehow destroyed your bacterial colonies those levels don't make any sense.
What NH3 test are you using? If it's an API I'm thinking your just misreading the color and you actually have a zero reading. Regardless, your lighting is just fine for keeping all species of clams and your CA/ALK is in the perfect range. I would say re-test those 3 levels and then you good to go and get addicted to clams like the rest of us
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