Are you feeding one full piece a day? That's quite a bit. You should break very small pieces off, about this size __ . I have that many in a tank and they get a tiny piece of the dry food once every other day and veggies once or twice a week. I never feed every day. Some people do, some people only feed twice a week. Once you get a good biofilm in the tank, the need to feed outside foods becomes more personal choice than necessity. Some people feed every day without issues, but it is possible to overfeed from what I've read and even with a feeding dish, the way they fling particles in the air, it lands on everything and you might eventually get critters/bugs in the tank from overfeeding (ask me how I know, LOL).
My suggestion on food is look through the forums, h4n sells sample sizes of the foods he carries. This is a GREAT way to save a ton of money so you don't buy foods your shrimps don't like. I bought two full size containers of Mosura CRS Specialty and Borneowild Grow (before I found sample sizes on here). They love the Mosura but don't like the Grow. So there's $15+ down the drain and it's only good for 4 months after you open it. As a matter of fact, if you want some I'll send you some. Better than it going to waste!
As for other foods, veggies are always great, mine get Zucchini, baby spinach, and kale. They'll eat peas, corn, green beans, lettuce, and much more, that's just all I have room for in my freezer.
I blanch them, separate them onto a plate and put in the freezer for an hour. Once they're crisp I toss them in ziplock baggies, dated, and they last for months in the freezer. I get organic and use veggie wash on them prior to boiling just to be extra cautious. Some people don't boil/cook them and instead just throw them in the freezer and that's enough to break the cells down to make them chewable. If they are too tough, your shrimp won't be able to eat them right away and then, I'm pretty opposed to leaving a piece of food in for 24 hours or more. Again, I've battled bugs! LOL! Dry food, I give them what they can eat in 2-4 hours. Veggies stay in 8-10 hours, but never overnight. This is just how I do it, others do it differently
I also feed Repashy Soilent Green which they ADORE. I made a half a batch and that stuff will go bad before I feed it all unless I get more like a thousand shrimp. LOL! The point is, the smallest bag would make you a couple of batches off the bat. Do some math and drop those down to 1/4 batches at a time and you'll be set for a long time. I believe I paid $7 or so for a small bag from a seller on here.
If you'd like I can give you a list of all the samples I've had (seriously, I have over 20 food samples here) and tell you what my PFRs love the most and what they can do without (says them). Or you can go to h4n and pick up some samples from him.
And don't forget, I can hook you up with the Borneowild Grow and Mosura CRS Specialty if you want to try those. The BW Grow I'll never go through in time (opened it in April, so a month left). I'm not going to toss it immediately after 4 months, but still, if they don't eat it, what's the point? Mine will eat it if they have no other choice. It's not like they don't bother it at all. It's just, there are other foods I feed they go nuts over, this just isn't one of them