Guppies are dying

Question
Hi, Nathan. I have 10 gal freshwater tank, and I am new to the fish keeping. I have the tank for about 2 month now, it started with high ammonia levels, low PH and fish loss, I did water testing, added PH Up, reduced feeding and got all readings under control, the fish was doing great and I even have 6 babies. I had to move the tank to a new place, so I transferred all the fish in a different container, poured water in a bucket, moved empty tank, brought back water and fish. Since water level was low, I had added some water, treated with conditioner, added aqua salt as directed. BUT.. I had 3 neon tetra who used to be bright orange and now pale with red streaks on the top fins, I have 2 fancy guppies who were laying down low and this morning one of them was floating on a side, still fully colored, the other fancy guppy is nowhere to be found, it lost all the color as of yesterday (i think its under the decor vase- dead). I had tested the water, 5-in-1 test came out normal, ammonia level is normal, PH level is normal (I get the same reading I used to 2 weeks ago). Did the stress of moving affected fancy guppies? what about neons? what can I do to keep my other 2 guppies, 2 Mollies, and 5 neons safe?
Thank you in advance

Answer
Hi Natalie,

Normally, the problem would be ammonia and nitrite problems. Since this is not the case, my best guess would be either physical stress or temperature shock. When you transferred the fish, there's a chance that you could have possibly injured a couple of them. Whether it's from rough netting or pouring, the fish may have been frightened, and crashed against an ornament or rock. This is actually quite common. (In one of the pet stores I've been at, the employee couldn't catch the species of fish I wanted, and spent over 3 minutes trying to catch it, injuring almost half dozen Cichlids. Eventually, I caught it myself.)

Moving the aquarium can be extremely stressful. The new location could be a different temperature, or if it's positioned near direct sunlight or a vent/window, this could be stressful.
It does not seem to be disease, judging from your description.

When you put new water in, did you use cold water? Using cold water is definitely not a good idea, because fish used to warm water should not have cold water changes. (Think of taking a warm shower and someone splashing a bucket of ice on you.) Always use room temperature water, or warm water checked with a temperature probe to be at 78F. Even though there's a heater, you cannot put cold water directly into the tank.

I recommend that you do 10% water changes every two days, and add a stress-reducing agent (often water conditioner will have this). This will prevent stress and death.

Don't use salt in the tank. Aquarium salt is completely unnecessary except in the treatment of Ich (a parasite). Additionally, Tetras cannot tolerate salt.

Good Luck, and Happy Fishkeeping!