• You are viewing the forum as a Guest, please login (you can use your Facebook, Twitter, Google or Microsoft account to login) or register using this link: Log in or Sign Up
  • You can now follow UKAPS on Instagram.

Soft water, plants and CO2 (or not)?


New Member
4 Jul 2020
So, I have gH and kH of 2, pH 6.4-6.6 out the tap. When I had my 240L tank (a couple of plants but nothing much and on playsand), pH regularly dropped to 6 or lower without co2 and I added a few squirts of potassium bicarbonate solution when I remembered.

I am now in the process of setting up a Fluval flex 57L and a 29L nano with Tropica soil, Aquascaper ferts and a range of Easy plants. I’m debating CO2 but am concerned about what would happen to my water and fish. If I add co2 am I going to end up with vinegar basically? I know the fish i’m planning will be ok in lower pH and my rummynose tetra bred in my previous tank so I know it should be OK. But I panic.

I can’t take in huge amounts of science anymore (despite graduating with a zoology degree exactly 19 years ago....the 19 years haven’t been easy ones on my brain cells). I wasn’t planning on CO2 but, well, you know how it goes with this hobby! I figure i’d best do it properly.

Can someone talk me through what co2 will do to my water, if it’s going to crash my filters (I know the plants will do a lot once established but I like to know my munchers in the media are ok) etc? I already have a SodaStream machine for drinks so I’m thinking that’s a reasonable option given the other option is the Tropica 60 or nano systems.


21 Apr 2020
Kuala Lumpur, Malaysia
My tap is 0KH and 1GH, 54TDS - very soft, so I understand your question.

The simple answer is your soft water has very little buffering capacity and therefore lends itself to PH crashes.

Fortunately the solution is also very simple. Raise your KH.

You can add dolomite or crushed coral, or crushed oyster shell to your substrate.

You can use any one of the commercial remineralisation products on the market like Aquadur or Equalibrium.

Or you can add dry Salts to raise KH, although I've not found none as effective as crushed coral as most don't dissolve well in water.

Personally I just hang two small bags of crushed coral in my tank for 20hrs after the weekly water change. Here the CO2 actually assists because it's creating extra carbonic acid in the water which quickly dissolves the coral, raising my KH just enough (probably to around 1KH) to get me through to the next weekly water change.
Last edited: