You know there are many people who say you should change this percentage or that percentage of water every day,week or month.It may be okay for them.You must change your water before it becomes dirty.The amount and frequency of your water changes depend on how many fish and how many gallons of water,also how much food your feeding them.Testing your water for ammonia,nitites,and nitrates will give you a good feel for how often and how much water you must change.Your water test kit is your friend.Use it OFTEN.It will confirm that you are keeping up with a proper schedule of water changes.
Well everything is right on point except for the PH and acidic levels are still too low i keep adding seashells but not seeing much of a change it went from 6.4 to 6.6. I know i also heard to use crushed coral but i couldnt find it at the petstore. Do I put the shells in the cartridge filter or just leave em on the bottom? I know ppl put the crushed coral in the filter.
If you want a significant effect on pH, the shells go into the flow path of the filter. That will get the calcium carbonate of the shell to interact more directly with the water. If you look at the sand they sell for a salt water tank, it will be composed of mostly crushed shell or crushed coral. From a chemical point of view, there is not much difference.
I think your PH is okay.If you want to raise your PH the simplest and best method is to place a few pieces of limestome or pieces of marble.The effect on the PH is slow and is not felt until several days have passed.If you want to raise your PH quickly,add some dissolved baking soda(sodium carbonate)until the desired PH is attained.Many years ago I used to use crushed oyster shells that I bought from bird feed stores.They feed the oster shells to chickens ,this helps them digest the grain they eat,its called grit.Be careful if you decide to use grit, make sure there is nothing added to it to make it smell better.Ask for PLAIN crushed oyster shells,natural not artificially made.Nature makes few mistakes.