ph and gravel

Question
I have a 29 gallon aquarium set up,  cycled, and ready to go for new fish.  I had a Betta which died a couple of weeks ago and I have gone ahead and cleaned all of his play things and done a few partial water changes since then.  All levels are fine except for the ph.  This has always been high, around 8.3-4.  I read several online posts that said as long as the ph is stable, that is the main thing.  My Betta seemed to do fine in this kind of water, but I want to know if I should try something that may lower the ph before adding new fish.  I have done various ph tests out of curiosity.  I noticed that my tap water, after being treated with dechlorinator, and left out for over a day or two just like it would be before pouring it into the tank, has a ph of 7.4.  However, the same water put into the tank rises to an 8.3-4.  I have a few decorations (cave, house, vase, rock) and some silk plants.  I also have a white gravel substrate that I bought from PetCo which was labeled as completely safe.  I have a strong feeling, though, that it is the gravel that may be causing the rise in the ph level (although I suppose it could also be the rock decoration I have that has a hole in it to swim through; I'm not sure what rock it's made from but it's only about the size of a hand).  When I vacuum the gravel, little specks that look like sand/salt/silt float around in the water sometimes in those areas.  In other areas, the rocks just suck up and fall back down from the vacuum without very much of that floating debris at all.  The plus side of the gravel is that it makes the aquarium look very nice and it is easy to see the fish fecal matter against the white gravel when it comes to cleaning.  The downside is that the ph of 8.4 is higher than what is listed as preferable for most freshwater fish.  As far as stability, it seems that the 8.3 - 8.4 is very steady as it's always that when I test it, but I wonder if water changes are extra hard on the fish since I'm pouring in 7.4 ph water which must later turn into the steady 8.3-4, but I don't know how long the change takes.  Do you think I should remove the gravel I have, test it to see if the ph lowers, and then purchase a different kind of substrate before I get new fish or should I just leave things as is?  The tank is perfectly ready to go apart from this one issue.  I want to make sure my fish are in as healthy an environment as possible, though.  Please let me know what you think.  Also, are there any safe tank mates for Bettas in case I get another one?  The last one I had was alone since I'd read they are loners.  I was thinking about maybe getting some Platies or something like that to accompany a Betta this time, but there is an awful lot of conflicting information online about fish compatibility.  Any help would be greatly appreciated.  Thanks!

Answer
Jeremy,
There are products on the market that help bring the Ph up or down,, and products that keep the Ph at a certain level. If these work, I don't know since I do not use them. It is true that steady Ph is better for the fish than unstable Ph. When you added the gravel did you rinse it thoroughly before putting it in the tank? Sometimes, if not rinsed well, the gravel and mess up the chemistry in the tank, but that normally does not last more than a few days. I would not remove the gravel since it is already in the tank and the tank is ready to go. I would try the products to help with the Ph, but most fish can adapt and do quite well as long as it does not get any higher than it is. As for the tank mate, there are a few that can be in the tank with a Betta, but it is not a sure thing. It really depends on the Betta. What works for some people will not work for others. Just do not ad any other Labyrinth fish since they will fight to the death. Also, no other fish with long flowing tails and/or fins such as guppies. The Betta will think it is another male and will fight that one as well. No molly fish because they are brackish water fish and need salt in their water. Male Betta's prefer to be alone, so any fish you add, make sure you keep a close eye on them to make sure there are no problems.