I agree that you need to increase the group of Corydoras, and given the space in a 65g tank a larger group like CrtyptFan suggested would be best. I might say 15-20, depending if any other substrate fish are intended. Same species, or mixed, up to you, but it is always best to have a few of each species. Cories are very social fish and will always be less stressed and thus healthier the more there are.
Moving beyond that, it will help to know the tank dimensions and the water parameters of your source (tap) water. The GH (general hardness) is most important, then pH. You may be able to track these down on the website of your water authority if you do not already know. And I'll mention here that whenever numbers are involved it is best to know the numbers rather than vague general terms that can mean different things.
Welcome to TFF.
The new Tank is 36 inches wide, 18 inches deep and 24 inches tall.
Based on my current water parameters with a dip stick test kit the tap is 0 for nitrites and nitrates, 6.5 Ph, 0 Kh, 0 Gh. My Current water parameters in my 25g tank are 0 Nitrates, 0 Nitrites, 7.0 Ph, 80 Kh, 30 Gh. I normally like my Kh around 120 and Gh around 30 and Ph closer to 7.5 so my tank is on the lower side of happy for my liking.
In the past I have used Baking Soda dissolved into distilled water to bring up both Kh and Gh. I am not sure if this is a great procedure but my fish have been happy thus far. I read about people doing this before buying my fish and getting them set up.
I also know that using the dip sticks are not entirely reliable and plan to switch to a better water testing kit moving forward. Suggestions?
I am not sure if this makes a difference but I do have a planted tank currently and would like to continue to have a planted tank moving forward. I have not used any sort of vitamins or fertilizers with these plants in 6 months and they seem to be thriving. I currently have 3 types of sword like plants and 3 bamboo looking plants and a moss ball.
I guess I have more questions to go along with what types of fish I should stock in my new 65g. I don't like to use the chemicals to get my water adjusted but with such a large tank I will be using a bit more tap water than distilled water, I feel I will need to use the chemicals to get my water properly adjusted. Suggestions on the best products or ways to get my tap water to be the right balance for my fish?
I was researching crushed coral for raising Kh and keeping Ph stable and wanted to play around with that but don't want to do anything to my current fish that could be harmful. Do you suggest trying crushed coral out? If not, what would you recommend?
Sorry for the rapid fire questions, I love these fish and want to do what's best for them while also enjoying them. When I originally picked out these fish it was because my baby loved to see the fish at the local aquarium and I thought it would bring her some joy to see them at home. These fish have slowly morphed into my other children as well as brought back good memories of my dad who used to have a few beautiful tropical fish aquariums while I was growing up.