Compost problems

We have been having problems germinating seed this year, especially lettuce so decided to do some pH tests. We used a standard pH and nutrient testing kit which uses liquid a pH test reagent.
The picture (sorry its a bit fuzzy) shows the various materials we have used. The second from the right is the ready made organic Coir based compost which is a very acid pH 4.5. This may explain the poor germination.

We have in the past experimented with mixing our own compost using Coir and our own sterilised topsoil. We tested our batch of top soil which came out at about 6 to 6.5 pH which is OK for our uses. The soil will to some extent act as a buffer holding onto moisture and nutrients while the seedlings are still in the modules as well as neutralising the acidic effect of the Coir
A small batch of our intended mix was made up and when tested it came out at pH6.0 which is perhaps a bit acid so we will by adding lime at about 50gm per 40 litres.
The other additives are perlite which both come out at about pH6to pH6.5.
The results of our pH tests, the mixed compost is extreme right showing pH about 6.5.