Sand loose its ability to raise PH?

[cpm6t]

I have sea sand as substrate in my 220g aquarium. I grow plants (mainly amazon sword types) very well there with low lighting.
My PH has always been around 7.5 - 8.0 and I was told that it is due to the sand that I've put in there. Even when I do 50% water change of ph7 neutral water, the PH would jump back to 7.5 - 8.0 in less than an hour. The sand has been there for about 1 year now.

Yesterday when I checked the PH (not doing any water changes before checking) the ph was about 6.8. I haven't changed anything in there for the last 6 months (except water changes of course).

Does sand loose its ability to increase ph with time?

By the way I prefer to have 6.8 - 7.0 ph water since this is mainly a peacock bass tank. Just would like to know how it happened.

 

[koltsixx]

To my knowledge true sand shouldn't raise your PH, the only sand that should is if you bought crushed coral. Even then I believe eventually the PH affecting coral will eventually run out of stuff to leach into the aquarium to raise the PH.

 

[duanes]

Some sea sand (if it is made of aragonite) is composed of crushed coral and shell, and contains calcium carbonate. Because of this component, it has the ability to buffer the water (temporarily hold pH at an equilibrium), but as the calcium carbonate is used up by acids in the water from fish waste +, the sand must be occasionally replenished, if you want the buffering to continue.
I use it in a FB reactor to help buffer alkalinity and find I need to replace a handful or so every few months, if the alkalinity or pH starts to drop soon after a water change.

 

[cpm6t]

Thanks for the input guys. I guess my sea sand has lost the ability to increase PH. That is good. I was not keen on keeping south american fish at ph 7.5 - 8 anyways.