Blackadder

I'd say the concrete water tank is the reason for the higher pH of your rain water, concrete will continue to increase the pH and hardness of your water for a long time. The pH from the water from your water tank probably changes depending on how recently its rained, drops after decent rain and slowly goes up when its dry. Your bore water probably has a lower pH because of the rocks etc it travels through in your area. Putting shell grit in the filters or water tank probably won't help because your pH is already going to high. Might be easier to use bore water for your fish tanks if you can, or collect rainwater into a separate container for your fish with maybe a bit of shell grit added to that.

H3.1 is LOSP treated, its the H3.2 that's usually used for outdoor stuff like decks

Why not just get a generator, you can get them quite cheap and it will run as long as your supply of petrol lasts. Also you could power more than just your fish tank if you have a power cut.

I think the chlorine everyone is talking about is chlorine bleach which is sodium hypochlorite. Sodium hypochlorite reacts with excess acetic acid to give of chlorine gas.

What are you doing with your probe for it to need replacing that often?

Gemstone bay is on the walk part way down to Cathedral cove

Oats mixed with some water and a bit of yeast, to give a thick not to wet mixture always worked well for me.

I don't know how you'd do the ro part, but the di bits easy, just add the resin to a filter

What you're already using should work, are you trying to raise it faster? You could use baking soda to get the pH of your tap water quickly to round what you want before adding it to your tank and keep using the shells, limestone or coral sand to buffer the water in your tank to stop it drifting.

I've done the coconut cave in the past too. I found you could crack the coconut straight down the middle if you hit it on the concrete after you've removed the liquid. You sometimes have to bounce (yes some of them will bounce) the coconut quite hard before it will break and it doesn't always work, but its quick if you don't want to saw.

Why don't you just get some new buffer solutions for your pH meter? Having to measure your pH some other way so you can calibrate the pH meter sort of defeats the purpose of having it doesn't it?

Why not try a strong salt solution, probably safer than boiling water which may not be so good for the seals on the heater or the cord even if its safe for the glass itself

Caustic soda would probably work.

Hold it against the white background of the color chart. You want water in the test tube only, you don't want water on the outside of the test tube or on the color chart.

Just paint some polystyrene and slip that in behind the tank, not quite as good as painting the glass but works ok. Any acrylic paints ok since its not going in the tank.