I have a few inexpensive hatchet fishes in the tank - if i add the acid to the sump a few drops at a time will that harm them? I just want to slowly lower the ph.I would. It would either make your peat last longer or make it not necessary at all. It will make the pH a lot more predictable. Any strong acid will do. Cobra venom sounds great. I use phosphoric acid, but if you can't find that, "API PH Down" is 9.6% sulfuric acid and pretty easy to buy in small volumes. Test it outside the aquarium to understand how many drops you need to add per gallon to your incoming water to get the pH to where you want it.
The tank pH will want to rise, so I would:
It took me a few weeks maybe to get it to where I know exactly how much acid to add to my incoming water. Once your pH is stable, then look at new plant growth starting on that date and decide when you're comfortable adding your canary animals.
- Assuming there are no animals in the tank, first get the tank to a desirable pH, maybe just 10 drops or so at a time.
- Water change with water at the correct pH.
- Measure your tank pH for the next few days. It will rise for a few days. You'll likely need to add more acid to your incoming water until you reach a point where the pH is stable in between water changes. It will always want to rise if you go longer than that.