And thatís the bit I donít get.. call me dumb etc, but why do people like George Farmer etc use normal tap water in their Planted setups knowing that it will exhaust the substrate..
Let me ask another question, if I didnít have the RCSís would the answer be the same?
Is itís because we are looking after the water for the shrimp rather than the plants?
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I did a bit of looking, and it appears George Farmer claims to have hard water. Unfortunately, that means different things to different people since there are actually two types of hardness. I'm sure you're familiar with this, but for the sake of others reading this, here we go
General hardness (GH) is a measurement of ions such as Ca++, Mg++, and Fe++. Other ions are pretty much inconsequential. This is what the majority of people now use to refer to soft or hard water - how much calcium and magnesium is in the water.
Carbonate hardness (KH) is the measurement of carbonates and bicarbonates, and this has a correlation with pH. Decades ago, this was what people meant by hard or soft water, so sometimes this gets confused by older literature or those who have been in the hobby for a long time.
Buffering substrates remove KH which lowers pH to a targeted pH. Most of the time this is a function of peat in the granules. We care about preserving this for sensitive shrimp, but it can also be helpful for plants as availability of nutrients *can* be better at lower pH.
George Farmer may not care about the lower pH beyond the initial startup of the tank. Once it is established, building up good mulm and bacteria, the buffering probably doesn't play as big of a role as the tank will slowly go acidic over time anyway. So to your question of having no CRS, it would only matter if you care about keeping the pH low for specific fertilizer or types of livestock.
The *advantage* of soil substrates is that they can bring certain nutrients into the root zone where plants can uptake easier and can prevent unwanted luxury uptake that leaves cannot prevent. In this case, it's not that soil is required or "better" than inert substrates like sand, but they offer a different way of maintaining your tank that could be more ideal than sand if done right.
The biggest key to all of this is "if done right". All the correct parameters and nutrient levels in the world won't help with poor tank hygiene, and guys like George Farmer literally write the books on good tank hygiene
Hopefully that helps, and all great questions!