Discus fry growth rate issues

[sunny]

My Discus fry are about six weeks old now and they still look tiny compared to what I've seen online. They're in a 40 gallon breeder with a sponge filter, bare bottom, and a heater holding 84F. I feed powder fry food three times daily plus baby brine once a day. Water changes are 30 percent every other day with dechlorinator and temp matched from a bucket. Parents got pulled two weeks ago into a 75 gallon downstairs. Some fry seem active and chase food, a few hang near the heater and barely eat. The room gets indirect window light about eight hours daily. Could stunted growth just be slow genetics or am I missing something obvious with feeding or water changes?

[swiftly]

Six weeks is still early but yours sound small if some barely eat. What size were they when you pulled the parents? I ran into this last year with a spawn in a 20 long, sponge filter at 86F, feeding beef heart mix and decapsulated brine plus powder four times a day. Growth picked up when I bumped water changes to daily 40 percent and added a small sponge pre filter on the intake. Fry hanging by the heater can mean stress or too much flow from the sponge filter bubbling hard. Also check nitrate, mine stalled around 20 ppm even with zero ammonia and nitrite on the test strips. Try target feeding in a quiet corner with lights dimmed an hour after.

[Dream]

I agree with swiftly that six weeks isn't the finish line, but fry hugging the heater while others eat well usually points to feeding or water quality rather than genetics alone. When I grow out fry I use a 30 gallon bare bottom tank, dual sponge filters on low simmer, 86 to 87F, and feed small amounts of powder fry food five times daily plus live baby brine twice. I change 50 percent water daily for the first eight weeks because fry poop loads up fast on bare bottom glass. If nitrate creeps above 10 ppm growth slows even when ammonia reads zero. Parent size matters but batch feeding response tells you more, if half the group attacks food within thirty seconds you're probably fine on portions. Consider separating the slow eaters into a small floating nursery box same temp same tank so they get first shot at baby brine without competition.

[Haven]

I wonder if the room lighting plays a bigger role than people admit. My adult Discus seem calmer with a timer set to ten hours on a low white LED bar, and the tank sits across from a north facing window so no direct sun hits the glass. When I had fry once they didn't grow fast either, though honestly I was traveling a lot and my neighbor fed flakes, which probably didn't help. Have you checked whether the heater is actually holding temp at the substrate level and not just at the surface? I read somewhere that bare bottom tanks lose heat faster near the glass edges. Maybe log morning and evening readings on a stick thermometer for a few days.