Houdel and Ted0 pretty much nailed this. To take it to a slightly higher level...
For perspective, lime juice has a pH of ~2.2; Coca Cola is ~2.3, distilled vinegar [5%] is ~2.4, Bud Light is ~4.3, cider vinegar is 4.5-5, municipal tap water typically is between 8.5 and 9.5 [to protect the piping it flows through]. A shallow sand well I had in Florida yielded a pH of just under 5. So for what it's worth, Coke has 100 times the H+ concentration of Bud Light!
If you want to estimate coolant-mixture pH, you have to raise 10 to the negative of the pH values of the solution components, multiply each of these values by its respective fraction in the mixture, add the resultant two numbers, and take the log of this sum. Multiply this by -1 to get pH. Simple, right?!?
Using a city-water pH of 8.5, anti-freeze at 10.5, and a 50/50 mixture [** means raised to the power of]:
[(10**-8.5) X 0.5] + [(10**-10.5) X 0.5] = 1.597 X (10**-9) = 0.000000001597. The log of this number is -8.796, so the pH is ~8.8.
...half city water...........half antifreeze................resulting H+ of the mixture
If you are on well water, your pH could be ~5-8.5, depending on your aquifer. The pH of a 50/50 mix with pH=5 is ~5.3! To get either of these to ~10 would indeed require adding something like sodium carbonate or bicarbonate.
If you get all this, you get an ATTABOY and 1/2 semester-hour credit in physical chemistry!
P.S.
Per re-read of the initial post, his 'reserve alkalinity level' was measured to be 3...units not provided. This isn't pH; it's some sort of measure of acid-neutralizing capacity. pH strips are needed to see what's really up. A 'ral' of 3 suggests he might have been ok.