Some birds have mild cases or severe cases of "pica"
noun
MEDICINE
noun:
pica
- a tendency or craving to eat substances other than normal food (such as clay, plaster, or ashes), occurring during childhood or pregnancy, or a symptom of disease.
"adults with pica tend to be highly selective"
Jasper had what I would deem mild pica and had to be watched constantly. She became impacted twice. Once when she ate a whiffle ball (many years ago), then more recently when she started eating the wood from her toys. The first time her crop became infected and $1,000 later, after Dr. visits and antibiotics and giving her Metamucil or almond butter every day for five weeks she was well. The second time the Dr. caught it early and she just had to have Metamucil and almond butter for a couple of weeks. She could never have a wooden anything after that. You should put you bird's poop in a plastic sack, if you have any suspicions that they are eating non-edible items, and squash the poop around looking for foreign items.
All I can say about the Timothy Hay and sea grass as substrate, is that you are playing with fire both with impaction and with Aspergillosis or another fungal infection. You sure don't want to deal with Aspergillosis. Good old paper is by far and away the safest best substrate for birds. None of the chips and stuff like it are safe.