Builder's fill will be even more alkaline than our regular sand, Cilla. Top dressing generously with compost mixed with some peat moss might help a lot. The Palm Gain fert will be ok for now, but if you can get some that is specific for acid-loving plants like azaleas that will be better. Palms need a lot of micronutrients that Ixoras probably don't want.
Foliar spray with Miracid will only be a very temporary fix, you need to amend the soil. Those Ixoras have now outgrown the potting soil they originally grew in, and are putting their new roots out into that awful builder's fill. Amending heavily and often with organic materials will help long term.
For the short term, get a box of Epsom Salts at the drug store or grocery store, and mix a tablespoon per gallon of water. Water them every couple of weeks with this, a gallon or so per bush. Should make them look better until you can get the soil improved. For future reference, the first book I bought when I moved to Florida was entitled "The newcomer's survival guide to gardening in Florida" (or something) and in the intro, the author stated "The soil here will hold the plant up, you have to do everything else.". Referring to the grey sand most people find in their garden, once they get away from the builder's fill dirt.
Find out if your landfill makes compost, and get as much as you can, to have on hand for whenever you're planting anything. The compost made by Sarasota County is excellent, and free if you go and load it yourself. I've even paid a teenager with a pickup truck and his friend to go get it for me. Cheap at the price!