Advice Please

[j mac]

Hi,
As a newbie I contacted the emergency forum several weeks ago as I was losing fish every couple of weeks. I took the advice given to carry out 50% water changes and to buy a decent testing kit. I bought the API freshwater testing kit. Over past few weeks all fish have stayed alive Test results from API have consistently been:
pH 7.6
high 7.8
Ammonia 0
Nitrite 0
Nitrate 20
Temperature 24
55l juwel tank
Currently have 9 fish - mixture of minnows, tetras and algae eater.My questions are these:
1)Do I need to lower the pH as regularly 7.8. If so any advice how? Have read mixed reviews on chemicals to do this? Or suggestions on fish that are happy in this?
2) How slowly should I introduce new fish - I have read do not double the amount that you currently have. (Then go back to daily water testing)
3)Also are the strip testing kits ok to check Cl, KH and GH or can you suggest another more accurate.
Thanks in advance for any advice !!

 

[fidjet2]

1- the ph of my tap and tank water is 8-8.2 you just have to introduce the fish more slowly. it is better if you have a stable ph then a fluctuating one
2- Wait a week after each introduction, only add a few at a time, but test frequently to make sure it is all ok
3- not sure on this one