PH dropping

[Kaza]

I do 30% water changes 3 times a week. Once the water has been aged it is around PH 7.4, GH 5, KH 2. I filter it through a RO unit and carbon. Then I add prime and 100mls of geo liquid to the barrel.
When I test the tank water before changing it the PH is 6.3 will this upset the fish when I then put water in that is ph 7.4 ? Also the KH is 0 should I add something to the water ? I am worried with KH on 0 that the PH may crash?
The fish seem very healthy and eating well.

[Trebs]

Generally, if your PH is lower than 3, the PH can crash. Keeping the KH at 4 should give you good stable conditions.

Is the PH 7.4 and KH 2 before or after using RO? I'm not sure if I'm reading it right.

[Kaza]

before RO KH 9, GH 9
After RO KH 2 GH 5 the TDS meter is on 350 which is high any lower and I get KH 0 and GH 1 or 2. There must be something added to adelaide water.
I want to bring the KH up but how do I do it? Shell grit? this will affect the PH as well? Also another problem is the water out the tap has a PH of around 7 after aging it is 7.8.
I wonder should I empty the barrel and clean it, could this be causing the higher PH? Also this afternoon I had my first spawn hatch so this is certainly not the time to play with the water. Yet I feel I need to get the KH up. before diaster hits!! Especially in the grow out tank.

[Trebs]

Probably the easiest way is to mix RO with straight tap water. Whatever ratio gives you a KH of 5 should be the aim.

It's important to note once your KH is around 4-5 your ph will come up to about 7.2 or so. IMO, this will be a good level to maintain long term for general keeping and raising fry. If your tank is currently at ph 6.3 or so and comes up to 7 you'll need a fair amount of bacteria. The problem with changing kh is that it doesn't have a sliding scale effect on ph (i.e. kh of 1-2 = ph 6-6.5, kh of 4-5 ph of 7-7.4). It's a straight jump. If you don't do something to add bacteria you'll most likely lose fish.

Best method if you wanted to change to kh 4 water is to fishless cycle a second filter in a spare tank at a higer ph then transfer the filter when the ph comes up. That way there is no ammo or nitrite spike. This is provided you have the extra filter, tank and heater.

If you do go down this path, having a plan is a must.

[Kaza]

Thanks Trebs I think I understand, so KH is tied in with the ph raising the KH raises the PH. Is it KH that is needed to help babies bones or GH?

My RO unit atuomatically adds a mix of filtered tap and ro water so I can very gradually adjust it. I am about to add a second canister filter to the tank which hopefully may help I can seed it from another tank and so cope with the extra bio load.

[Trebs]

KH and GH are different types of hardness. There is certainly plenty of liturature if you want to find out more. For what you are aiming to do, as long as you know the KH and how it effects PH, that will be enough.

As for fry development I've read a lot of things about what ph and conditions are best. As long as you change water and use at least part straight tap water with the RO it should work well. Main thing is to have conditions as stable as possible. That's the most important thing in terms of water condition for fry.

Seeding the extra filter will be good but getting it fully cycled will be the best option. Maybe hook up the canister to a bucket and fishless cycle that?