be warned, if you follow this link the page has some script on it that freezes my laptop for around 30 seconds before giving a dialogue box asking if you want to stop the script running. After I click yes my laptop runs fine.
Acid blend is a combination of tartaric, citric and malic acid (proportions vary depending on source). Mainly its used to adjust the acidity so just using citric will probably be OK but I'd guess using a blend improves the flavour in some way.