Hello,
I very much enjoyed Ned’s detailed suggestions for switching to a planted tank (last post 06/06/06). Thanks Ned. I have additional questions about the water issue.
MWRA aims for a pH of 9.1 with an alkalinity of 40 mg/L, and the GH of the supply is naturally <1 (MWRA claim 7 ppm at the source, 15-20 at the tap). To achieve this pH, they dose the supply with sodium carbonate. What they aim for is in fact precisely what I measure at the faucet in Somerville and I would expect that many, if not most people on this forum deal with the same water. The easiest way to lock the pH at 7 for a community tank is with phosphate buffers and for good reasons. The pKa’s of phosphoric acid are pKa1 = 2.1, pKa2 = 7.2 and pKa3 = 12.6, which are obviously ideal for a neutral buffer. However manufacturers do not recommend using phosphate buffers with plants. I assume that’s because the plants would soak it up, making the pH crash (or are phosphates toxic to aquatic plants above a certain threshold?).
Obviously a large number of people have been very successful at keeping planted tanks with MWRA tap water. I should add that I now only keep tetras and other soft water-loving fish in my 36 gallons tank, and would aim for a pH of 6.5.
What’s the most reliable way to achieve this?
- Can phosphate buffers actually be ok?
- CO2 injection seems like the most logical and preferred option. How does one maintain a fairly constant pH using CO2 injection starting from tap water with the aforementioned specs, taking into account 30% weekly water changes, etc? (as an aside, is peat of any help to stabilize the pH, since it releases organic acids, or do people simply use it to soften the water?). I understand that the pH goes up and down naturally in a planted tank, but it still has to be within reasons for the fish to be happy, right?
- Non-phosphate buffers? They amount to replacing CO2 with another source of acid (I believe the Seachem acid buffer is sodium bisulfate). Once the bisulfate is consumed, all that’s left is carbonate and CO2, and as CO2 is gradually desolvated and released into the atmosphere, the pH creeps back up. Which takes us back to CO2 injection… Continuous CO2 injection certainly beats having to add bisulfate every day, notwithstanding the accumulation of sulfates. Does anybody use Seachem acid buffer as an alternative to CO2? Why do they even sell the stuff? By nature it makes for an unstable system.
I would be grateful for your advice and other successful aquarists’ experience with plants and MWRA water.
Thanks very much in advance.
Jul