Утром проверили жёсткость воды и обнаружили аммиак.

Russian often omits the subject when it is:

• obvious from context,
• unknown,
• or not important.

The forms проверили and обнаружили are past tense, plural, so literally they mean checked and discovered with an implied they.

In English, this can correspond to:

• They checked the water hardness and found ammonia
• The water hardness was checked and ammonia was found
• We checked... if the context makes that clear

So the sentence deliberately leaves the doer unspecified or understood from context.

In Russian past tense, verbs agree with the subject in gender/number:

• masculine singular: проверил
• feminine singular: проверила
• neuter singular: проверило
• plural: проверили

Since the subject is omitted, the plural form suggests an implied they or we.

The same applies to обнаружили.

Утром is the form used to mean in the morning.

It comes from утро (morning), but here it is in the instrumental singular:

• утро → утром

Russian often uses this instrumental form for times of day:

• утром = in the morning
• днём = in the daytime / during the day
• вечером = in the evening
• ночью = at night

So утром is not the subject; it is a time expression.

Because воды is in the genitive case after the noun жёсткость.

This is a very common Russian pattern:

• X of Y → X + genitive of Y

So:

• жёсткость = hardness
• вода = water
• жёсткость воды = hardness of water / water hardness

Other similar examples:

• цвет машины = the color of the car
• начало урока = the beginning of the lesson
• температура воздуха = the temperature of the air

It means water hardness — the amount of dissolved minerals, especially calcium and magnesium, in water.

Grammatically, it is literally:

• жёсткость = hardness
• воды = of water

So Russian expresses it as the hardness of the water.

Аммиак is a masculine inanimate noun, and in Russian the accusative singular of masculine inanimate nouns is usually the same as the nominative singular.

So:

• nominative: аммиак
• accusative: аммиак

That is why обнаружили аммиак means found ammonia with no visible change in the noun form.

Compare:

• вижу стол = I see a table
• обнаружили аммиак = they found ammonia

But with animate masculine nouns, accusative often matches genitive instead:

• вижу студента

Both проверили and обнаружили are perfective verbs:

• проверили ← проверить
• обнаружили ← обнаружить

Perfective is used because the sentence talks about completed actions:

1. they checked the water hardness,
2. then they discovered ammonia.

This is exactly the kind of sequence where Russian usually prefers perfective verbs.

If you used imperfective forms, the meaning would shift toward process, repetition, or background action.

Most naturally, it describes a one-time completed event, especially because:

• утром gives a specific time frame,
• both verbs are perfective,
• and the sentence reads like a report of results.

So it sounds like: In the morning, they checked the water hardness and found ammonia.

If you wanted habitual meaning, Russian would usually signal that more clearly.

Because this is a normal coordination of two verbs with the same implied subject:

• проверили
• обнаружили

They are joined by и (and), and in this kind of simple sentence Russian normally does not use a comma.

So:

• Утром проверили жёсткость воды и обнаружили аммиак.

No comma is needed.

Yes. Russian word order is flexible, though the original sounds natural and neutral.

Original:

• Утром проверили жёсткость воды и обнаружили аммиак.

Possible variations:

• Жёсткость воды утром проверили и обнаружили аммиак.
• Аммиак обнаружили утром, когда проверили жёсткость воды.

But these either sound more marked, more literary, or shift emphasis.

The original sentence is the most straightforward, report-like version:

• time first,
• then action 1,
• then action 2.

Yes.

• жёсткий = hard, rigid, harsh
• жёсткость = hardness, rigidity, harshness

The noun -ость often corresponds to English -ness:

• мягкий → мягкость = softness
• скорый → скорость = speed
• жёсткий → жёсткость = hardness

So жёсткость воды is literally the hardness of water.

Yes. In many texts, Russians write е instead of ё, so you may see:

• жёсткость
• жесткость

Both represent the same word, though жёсткость is the more precise spelling.

This happens a lot in Russian writing:

• всё / все
• ёлка / елка
• жёсткость / жесткость

As a learner, it is good to know that ё is often omitted in ordinary print, even when it should technically be there.

Yes, depending on context.

Because Russian omits subjects so often, проверили and обнаружили can sometimes be understood as:

• they checked / found
• we checked / found
• a general passive-like reporting style

For example, in a lab report or conversation among coworkers, it might naturally mean: We checked the water hardness in the morning and found ammonia.

Without context, the safest grammatical explanation is simply: plural past verb with omitted subject.