Just to check - that 11.38mg/l, was that just calcium or calcium carbonate? Water companies have the habit of quoting either just calcium or both, and for fishkeeping purposes we use the calcium carbonate unit or german degrees.
If it is just calcium, that 11.38 converts to 28.24mg/l calcium carbonate (CaCO
3) and 1.6 german degrees.
Both of these are very soft. And your KH (carbonate hardness) is also going to be very soft. You could ask a shop to check the KH of your tapwater to be sure.
In the short term for cycling, you need to boost the KH as 1) the filter bacteria need carbonate to multiply and 2)you are in great danger of a pH crash. The simplest way to boost it is by adding baking soda (nor baking powder) sold in the home baking section at the supermarket. Use a 15ml spoonful for every 50 litres tank water. Keep an eye on your pH and as soon as you spot it dropping, add some more. Or buy a KH tester to keep an eye on that; it should be above 6 german deg/110mg/l for cycling. At the end of the cycle you will need to do a 100% water change to get rid of the sodium before getting fish.
Once you have fish, I would add something to increase the hardness slightly. Unless you want hard water fish you would only need to boost it a bit. With the low hardness you have, I don't think using crushed coral or limestone rocks would increase it enough. I would seriously think about using remineralisation salts, the ones you have to add if you use 100% RO water. A couple of examples are
Kent RO right and
Tropic Marin remin tropical making sure you get the freshwater versions not the marine.
You would use these by adding enough to raise the GH and KH to at least 4 german deg/ 72mg/l. Ideally, add to a bucket of water and test before adding it to the tank. And you'd have to be sure to add the right amount of salts to give the same reading at every water change.
The other option would be to choose only fish that prefer very soft water such as those form the Amazon. And do a couple of water changes a week to keep the KH topped up. The acids made by the nitrogen cycle and fish waste use up the carbonate, so in your circumstances it would need topping up quite frequently.
