lime stones and corals from beach as filter media...is it ok/safe?

guys i brought with me some lime stones and corals from rosal beach resort. i am still looking for some sources if safe siya gamitin as filter media for koi pond but i only got one negative feedbacks and mostly ok daw. pero di ko pa nilagay sa filter chambers kasi nga i want to make sure. sabi sa mga nabasa ko ok daw ung lime stone (calcium carbonate) sa pond kasi it makes the water hard and it serves as a buffer sa ph level ng pond mo. ginagawa nyang ma maintain above 6 ung ph level ng pond water.
help naman if may experience kayo mag lagay ng lime stones sa pond nyo.

ph usually ang common affected if gamit ka og limestones... not advisable for concrete ponds... usually ginagamit ang liming for mudpond as to produced a good algae, sportfish production... mao ra ni aqng ikaambag...

as to sa corals... not sure if you can use it as a filter and NEVER use it as a design sa Koi Pond nimo because probable nga magisi ang skin sa imong kois...

ah ok so dili nalng nako ni ibutang salamat bai vic. hehehe