Hi Jeff,
40 gallons is a bit small for 4 orandas, unless you plan on doing water changes 80% at least twice a week!
As far as ph is concerned goldfish prefer a more alkaline environment so 7 being neutral to 8+ . 
Where are you located? Goldfishconnection.com has a great product called buff it up.
The aquarium pH is directly related to carbonate hardness levels in the aquarium. Carbonate hardness is the buffer that helps hold the pH up.  It's a good idea to determine also your carbonate hardness level. One of the best ways of dealing with pH issues is to use something like a alkaline buffer which is a calcium carbonate, magnesium carbonate buffer. It will raise pH but it will also raise the carbonate hardness. Liquid pH buffers such as pHUP and the like are kind of temporary fixes. They tend not to address the problem of the carbonate hardness levels. Baking soda also not a terribly good pH solution. It's a temporary solution. It's a sodium bicarbonate. Otherwise shell and coral material, in this case crushed coral can be used in bags and filtration. Crushed coral will help with buffering the calcium carbonate levels as well as the pH. The problems with using crushed coral you can't really control what it's going to do. So you have to be very careful not to add too much. As always when dealing with pH issues it's very, very important not to raise pH too far too fast. You generally don't want to go more than about half a degree in any twelve to twenty four hour period. So if you have a long way to raise your pH try to do it over a period of days.

 4 Orandas
Minimum Tank Volume: 360 litres
Minimum Tank Size: 4ft
Water Temperature Range: 18-22°C
Water pH Range: 6.5-8.5
Water Hardness Range: 6-16 dGH(not that important)

Your pH is a tad low ; don't bother with buffers;, like as not you'll do more harm than good.
Check your water parameters when the cycle is complete, then and only then will you know if you have a problem
 
 You'll need to   upgrade the tank in a year or two's time

Hey thanks everyone.sorry for the other post.i am planning to keep just 3 orandas.my filter turnover rate is 500 gallons per hour.I don't want to invest in another tank right now.can I add a big sea shell after boiling it to the aquarium so that it will enhance the look of the aquarium as well as increase the ph a bit further or do I have to wait till the tank is cycled to see whether my ph will increase after cycling.thanks again guys.I am currently staying in Kuwait.we don't have much options here.i don't want to add solutions to increase ph.i want some permanent natural solution.