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The diet is unlimited hay.
They can have one cup of veg per pig per day. Safe daily veggies include a small piece of lettuce, a coupe of sprigs of coriander/cilantro, a slice of bell pepper and a slice of cucumber. (The guide I added in shows a sample plate with amounts)
They can have one tablespoon of plain guinea pig pellets per pig per day.
Most calcium comes into the diet via pellets and water. So pellets do need to be kept strictly limited and water should be filtered (particularly if in a hard water area).
Other high calcium veggies include parsley, kale and spinach - these should also be kept limited and not given more than once a week in very small amounts
Too much calcium, can disrupt the balance and cause bladder problems such as sludge and stone formation.
Fruit and carrots are not suitable to be given every day. They can be given as a very occasional treat but no more than once a week (they don’t actually need to ever be in the diet though)
Brassicas such as broccoli or sprouts can cause bloat so be careful with quantities of those
Long Term Balanced General And Special Needs Guinea Pig Diets
This is another guide that you may find useful.
Edible And Forbidden Veg And Fruit List With Vitamin C Grading
Do ensure that you introduce any new veg into their diet slowly. Any new items can cause digestive issues so you need to be careful not to overload the system by either feeding too many new things at a time or by feeding too much. Only introduce one new thing at a time and ensure they are ok with it before introducing anything new.
This guide explains
How to Introduce New or Reintroduce Regular Fresh Food Safely - The Rules
