Unexplained pH and kh crashes.

I have a couple tanks the have recently been going through crashes every few days after WC.

WC it is at 120kh and 7.4 pH that is also right out the tap.

Few days later pH is 6.2 and kh is 0.

Never had a problem before then in the last few months it has been this way. With 2 separate tanks every time it is the same on both and same time frames to get there.

Any thoughts on how to stop this and keep it back to the way it was? Used to stay at the 120 and 7.4 as I had Cuban gars and had to keep it stable so I watched it closely.

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duanes said:

A pH crash is an indication that metabolism by products (acids from fish urine, rotting food, filters overwhelmed with gunk, too many (too large) fish for the size of the tank, etc) are soaking up the buffering capacity of your water.
More water changes, cleaning filters, vacuuming, are usually the remedy.
It may be that as your fish have grown, your normal routines are now, insufficient.
What is your normal water change routine?
How often do you clean filters?
Feeding amount and frequency?
Stocking level?

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Pre Filters are cleaned every week to 2 weeks. I have a sponge on one with light community stock and heavy plants. No ammo or nitrites in it and nitrites are at 10ppm. Light feedings on this tank. WC is 1-2x 50% weekly.

The other one has heavy bioload with stingrays but not in numbers. Only 2 large rays and a large aro in a 180gal. They have an upgrade being built. This tank has daily medium feeds with 1 day off a week. WC 2-3x 75-80% weekly.

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I have had the rays with more stock on the same schedule without issue in the past. It is only recently after removing fish have I had an issue. The rays have not put on to much size but some.

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Come to think of it a few months back I took out the crushed coral I had in the sump for my cuban gars. Didn't think I would need it for the rays. Might have to add it back in. Didn't remember that and it could explain why I have been having pH issues lately.

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