Looking to get others opinions on what may be going on. This morning I found 3 of my platys dead. Everyone has been swimming around actively, eating, no signs of labored breathing. Appearance of all fish have looked fine. The other fish that are in the tank are also showing no signs of illness or anything being wrong. Here is some information on the tank, my ammonia when testing was slightly elevated which I believe was probably from the 3 dead fish in the tank.
1. Size of tank? 50 gallons
2. Water parameters
a. Ammonia? .25 ppm
b. Nitrite? 0ppm
c. Nitrate? 5ppm
d. pH, KH and GH? 7.4, 3, 8
e. Test kit? API master test kit
3. Temperature? 78
4. FW (fresh water) or BW (brackish)? fresh water
5. How long the aquarium has been set up? May
6. What fish do you have? How many are in your tank? How big are they? How long have you had them? 4 angelfish added in May, 2 bolivian rams added in May, 6 black widow tetras added in May, 13 corys 7 added in May 6 added a few weeks ago, 2 rubberlipped plecos added in May, Platys started with 6 in May 4 females 2 males lost one of the orginial females about a month ago. About 2 months ago added 2 more females, lost one while changing over substrate from gravel to sand. Two weeks ago added 3 female platys, lost one of those 3 within a week of adding. The 3 that I found dead this morning was two of the orginials added in May and the other one was the remaining female that was added two months ago
7. Were the fish placed under quarantine period (minus the first batch from the point wherein the tank is ready to accommodate the inhabitants)? No
8. a. Any live plants? Fake plants? Live plants
b. Sand, gravel, barebottom? sand
c. Rocks, woods, fancy decors? Any hollow decors? Maylasian driftwood 4 pieces, a few river rocks
9. a. Filtration? 2 sponge filters one in each corner combined rated for 100 gallons
b. Heater? yes
10. a. Lighting schedule? What lights are used? Lights on at 11:00am off at 9:00pm
b. Any sunlight exposure? How long? no
11. a. Water change schedule? weekly
b. Volume of water changed? 50%
c. Well water, tap water, RO water? tap water
d. Water conditioner used? was using API stress coat just changed to tetra aqua safe plus
e. Frequency of gravel/sand (if any) vacuumed? weekly
12. Foods? Flake food, occassional treat of frozen blood worms
How often are they fed? Flake food daily, frozen blood worms once a week or so.
13. a. Any abnormal signs/symptoms? no
b. Appearance of poop? normal
c. Appearance of gills? normal
14. a. Have you treated your fish ahead of diagnosis? no
b. What meds were used?
15. Insert photos of fish in question and full tank shot if necessary
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Also recently added more live plants to the tank, although don't think that should have had any effect.