lowering my ph , kh, gh,

[adhdan]

1300l dirt/sand planted tank with 150l sump

My tap water is very hard PH 7.8/8 KH11 GH20

I dont want another RO unit so i have been using collected rainwater to reach my target of PH 6-7 KH 2-4 GH 4-6

Ive been transferring water for a few days and ive got the tank water down to PH7.4 KH6 GH12,

My question is.. is there a delay in the PH coming down or does it equalize within minutes/hours of water changes? Should i expect the PH to suddenly swing or become unstable when i reach a certain water softness? Ive halved my KH GH and the PH has only come down 0.5 which i thought it would come down quicker because the rainwater tests at 6.6


Any advice welcome, just want to make sure i don't suddenly swing the tank
Thanks

 

[Byron]

The three parameters are closely connected. The pH is governed by the GH and KH, along with other factors like dissolved CO2. But the GH at 12 and KH at 6 are still strong enough to buffer the pH avoiding fluctuation. However, in the aquarium with biological processes also affecting the parameters, things can change. So far as I am aware, there is no way to ascertain exactly what, it depends upon the biological forces at work here.

Diluting hard water with "pure" water like rainwater is proportional. Simple example, with half tap and half pure, the GH and KH will be reduced by half. The pH will do whatever the GH/KH and other factors influence it.

Remember you need to prepare identical water for every water change. Otherwise, the W/C will probably result in a larger than good shift in parameters which may harm the fish. I suspect you know this, but it doesn't hurt to mention it.

 

[adhdan]

ok thanks, i'll carry on changing water then.
Ive got auto water change from a rain barrel but auto top off is from the mains supply, if i work out how much i lose to evaporation each day i can AWC 2x the amount of rain in. gives me a starting point