If i add peat to really hard, slightly alkaline water, how long will the peat buffer? Should i put it under the substrate and in the filter?
In order for iron to be available from a substrate, you need to use a clay, soil or iron containing substrate additive together with a small amount of organic material such as peat. The organic material provides nutrients for anaerobic bacteria to reduce insoluble iron (ferric) to soluble iron (ferrous). It also releases humic acids which are natural chelator chemicals which lock onto positively charged chemical ions like Fe++ and make it available in the water. These humic acids also help to buffer the pH in your aquarium to a good value.