Mystery die off...

So I started off with 10 black neon tetras and now I only have one, I also lost two German blue rams (who were about to spawn) and a guppy  . I did home water tests and nothing seemed out of the ordinary with the tests, I took some water to petco and the only thing was a slightly high pH, but she didn't seem too concerned about it. The water was a little cloudy, most of my fish seemed fine but a couple were lethargic. I did a big water change and vacuumed the gravel, added some stress coat. Now my tank is clear and no other fish have died. So I don't really know what was up  

On the bright side, having to take everything out of the tank is a good time to try a new scape    
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How high was the ph? Btw. Post that tank picture in the gallery. Nice tank!

Im not sure, from what she said it was not very high, but I don't really trust them. Could high ph cause these problems?

Black neon tetras
Temperament: Community
Family: Characidae
Native To: South America
Diet: Omnivore
Adult Size: Up to 1.5"
Temperature: 72° - 82°F
Water Parameters: pH 6.0-7.0; KH 4-8
Care Level: Easy
Tank Size: 10+ gallons
Scientific Name: Hyphessobrycon herbertaxelrodi
Environment: Freshwater

Ram cichlids
Minimum Tank Size: 20 gallons
Care Level: Difficult
Temperament: Peaceful
Water Conditions: 72-79° F, KH 5-12, pH 5.0-7.0
Max. Size: 3"
Color Form: Blue, Orange, Red, Yellow
Diet: Omnivore
Origin: Farm Raised, Thailand
Family: Cichlidae

Was ph higher than 7.0?

A "slightly high PH" would not have resulted in the death of so many fish over a short period of time like that (I'm assuming it was a short period of time).  PH doesn't kill fish, rather PH swings kill fish.  That said, fish can suffer osmotic shock after being introduced to water with a big PH difference (and because of the difference in minerals in the water, not the PH itself), but this happens within several weeks of introduction.

If your PH was slightly high then it's unlikely it would be swinging.  Your water has 5 dKH and 9 dGH (from my testing).  That GH is a bit on the high side for our area - great for platies and other livebearers, but not so much for fish that prefer softer water like tetras and rams. I didn't test your water for PH; I assumed it was in the 7.6 - 8 range given your KH.

How long ago did you introduced the fish that died?

The fish that died have been in there for months, they were really big healthy tetras and the rams were healthy as well. (this did happen in a short period of time) and I had not changed anything in my cleaning/ water change routine

Then it's definitely not a PH issue. How often do you do water changes? Did they die close to a water change?

Ammonia and nitrite are both 0? What are your nitrates?

Ill do a test tomorrow and get back to you, but I water change every 1-1.5 weeks. I think I did add water near when this happened.

Nitrates were just below 40 and the nitrite was a little high 0.25

Then that's your problem. The tank is experiencing a cycle. You should not see any nitrite ever in a cycled tank.

how do you lower nitrates? nitrites you lower with water changes right?

The nitrates are ok, the nitrite is not. Seachem prime may help with nitrite. It certainly helps with ammonia, which will reduce nitrite for sure, but not right away. A large water change will help too.

I haven't tested it since the huge water change so we shall see.

If I am not mistaken Nitrites are a sign the tank is cycling and usually coincides with moderate to high ammonia levels or bacterial die off?

Ammonia was 0

MorganEA do you still want those fishes, I have?

The presence of either ammonia or nitrite indicates the tank is still cycling. I'd test again soon for both of them to be safe.

Yes SirWes I just got my 20 leak tested I just need to buy some substrate

I could use some fish after this lol

You can share with your sister.