One of my fish died today

Iv had him for about 4 years, maybe more.

As my fish water keeps turning very acidic (pH 5), iv been adding carb soda to put the ph up. I did this 2 days ago, then from that day he was looking a bit sick (sitting at bottom, and not eating). Toady i checked on him and he was on his side on the bototm of the tank. Was this because i changed the pH too quickly? or? maybe had a pebble stuck in his throat? My other fish didnt look like they were effected.

I'm so sorry Nick and if I were to guess, I think it has everything to do with your ph. I know what you're going through because my ph plummets quickly but instead of relying on baking soda which only raises it for a short time before it falls again - I now have crushed coral in each tank. It's been very successful at keeping the ph stable at 7.8 and my fish are benefiting from this stability.

I nearly lost one of my guys who just couldn't take the constant fluctuation because it's only been recently that my kh has dropped to a level that is unstable - for years it remained at a constant 7.5... They become stressed quickly because of the alteration between acidic water to alkaline water and that's when they fall ill or worse case scenario is they literally burn to death because ph below 6.0 is like an acid bath.

So if you can, try to get some crushed coral into your tank - either in the substrate or better yet, in your filters so the water constantly runs through it and your ph will rise and stay there