I don't have cichlids but I have been making a custom fertilizer to address issues Have seen in my small 100% RO water Tank. So the following should be helpful.
Yes I did read that too but i already filled my substrate. Depending on how much it would take to increase the hardness that could be an option. Thanks!
At the desired PH adding crush coral to the tank will not increase hardness sufficiently to reach the desired GH. crushed coral will only dissolve when the PH is less than 7. It will not dissolve when the PH is above 7. However crushed coral in an aquarium would prevent the PH from dropping unexpectedly.
The ingredients listed on the bottle are calcium chloride, magnesium chloride, potassium sulfate, sodium chloride, iron sulfate, Aluminum sulfate, iron sulfate, and potassium iodide. Most have a biological function and fish need them. Aluminum sulfate has no biological function. So the most important parts Calcium and magnesium to boost GH, sodium potassium. The rest are needed in small quantities and your fish will get most of those from the fish food. And they may already be present in your tap water.
So you could buy a chloride based GH booster or purchase calcium chloride and magnesium chloride and make your own GH booster. All the ingredients I have listed are available on line and or in stores. And if you can avoid shipping costs you could safe some money. Or you can make your own Gh booster with Ca and Mg chloride and add potassium to that and sea salt. That add as much as needed to achieve the desired GH. Than add baking soda to achieve the desired KH and PH. This not really an accurate recreation of cichlid lake water. There are typically many more elements in water but most will have Littleton no impact on fish health. I prefer sea salt over ordinary table salt because it has about 100 different elements in it including iodine. bromine, lithium cobalt and other nutrients fish need in small quantities.
This site for an alternative product lists calcium magnesium ratios for two different rift lakes and a sodium potassium ratio. It might be helpful in figuring out a good recipe. It is probably not important to get the ratios exactly right for cichlids.
This fertilizer calculator may also be helpful. it has calcium chloride and potassium sulfate in pull down list. You can use it to help tune your recipe. And it can predict the amount of baking soda to add to achieve a targetKH.