GH KH & PH Query - crushed coral

[Fishtank]

I have become sloppy about doing my PW changes due to several intense issues within the family right now that demanded my attention, back a year or so ago I added crushed coral in the hopes of buffering my KH and GH slightly (mostly just to buffer KH though) as my tap water sits at GH - 3 / KH - 3 (believe quite a low 3) & PH - 7.4. I last did a Part water change in August so today with some spare time I tested my parameters and set about a new part water change. The results were very surprising and came out at GH - 9! KH - 3 and PH - 7.4. I was confused by this as my GH has gone through the scale which is not surprising with the lack of pw changes but what was surprising was that none of the other parameters changed at all.

My main question is: Is the crushed coral actually doing anything? Maybe I should take it out and work on getting my GH back down to a normal rate for the fish I keep, OR should I keep it in there and do PW changes more frequently so that the buffer is there but the parameters stay around my tap water parameters instead?

I added the crushed coral initially as my LFS moaned about my KH being so low, has anyone got any advice? I changed 75 litres about an hour ago, I will test around 5pm and do another tonight until the GH comes down.
Please help me, I don't know what to do for the best

[black ghost]

You don’t actually have a problem.

A KH of 3 isn’t too low. I’ve kept fish for over 50 years, always with tapwater of KH 2-3. KH is only required for two reasons… neutralising the various acids produced in a fish tank to prevent the pH from dropping, and providing a source of carbon for nitrifying bacteria. As long as it goes no lower it’s fine.
A small amount of coral gravel will very slowly dissolve… enough to maintain a consistent KH as the various aquatic processes use it.
GH doesn’t get “used” so your crushed coral has gradually increased it. KH does get used, so your crushed coral has been replacing it as it has been used. pH won’t normally change as long as there’s enough of a KH presence.

My advice would be to get back to weekly water changes. Then you’ll have nothing to worry about. The crushed coral will prevent the KH from dropping further, which will prevent the pH from dropping.

[Fishtank]

Will regular PW changes lower the GH back to the normal range as it's considerably lower than 9? thank you for your reply, I didn't know what to do for the best but I know that my tank has dropped in PH before now which was the reason I added the buffer to begin with

[black ghost]

Sounds like you need the buffering from the KH, but now you know you have enough coral and it’s doing the job. Water changes will return the parameters to those of the tap.
But fish need regular water changes for several reasons. It’s not just about hardness and pH.

[Fishtank]

Thanks, I will keep up with the water changes until it stabilises around the tap parameters and then keep on top of it, what a nightmare it has been. I understand the other reasOns for water changes, I will keep on top of them