O aquarista verifica cada vez mais o pH.

Aquarista means aquarist: someone who keeps, studies, or works with aquariums and fish.

A useful detail: aquarista has the same form for both a man and a woman. The article shows the gender:

• o aquarista = the male aquarist
• a aquarista = the female aquarist

O is the masculine singular definite article, meaning the.

So:

• O aquarista = the aquarist (male)
• A aquarista = the aquarist (female)

Even though aquarista ends in -a, it is not automatically feminine. This is one of those nouns where the article tells you the gender.

Here, verifica is best understood as checks.

Although verificar can sometimes look like the English verb verify, in everyday Portuguese it often means:

• to check
• to inspect
• to examine
• to monitor

So in this sentence, verifica is more natural as checks than as verifies.

Portuguese often uses the simple present for habitual or repeated actions.

So O aquarista verifica... suggests something like:

• the aquarist checks...
• the aquarist is checking regularly...
• the aquarist checks as a routine

If you said está verificando, it would sound more like something happening right now, at this moment:

• O aquarista está verificando o pH. = The aquarist is checking the pH.

In your sentence, the simple present fits well because it describes an ongoing tendency or habit.

Cada vez mais means more and more or increasingly.

It expresses a gradual increase. Depending on context, it can refer to:

• frequency: more and more often
• degree/intensity: more and more
• quantity: more and more

In this sentence, the most natural idea is probably more and more often:

• O aquarista verifica cada vez mais o pH.
• The aquarist checks the pH more and more often.

In Portuguese, adverbial expressions like cada vez mais can often be placed before or after the object.

So these are both possible:

• O aquarista verifica cada vez mais o pH.
• O aquarista verifica o pH cada vez mais.

The version with cada vez mais before o pH sounds very natural and keeps the idea of increasing frequency tightly connected to the verb verifica.

Very roughly:

• verifica cada vez mais o pH = emphasizes the increasing action of checking
• verifica o pH cada vez mais = also correct, slightly different rhythm/emphasis

Portuguese uses definite articles much more often than English does.

So o pH is completely normal and natural. It means the pH.

Even when English might say just pH, Portuguese often prefers the article:

• medir o pH
• controlar o pH
• alterar o pH

Also, pH is treated as masculine in this expression, so the article is o.

In Brazilian Portuguese, pH is usually read as the names of the letters:

• pê agá

So the sentence would include something like:

• o pê-agá

This is different from English, where you might say the letters in an English way.

No. Cada vez mais is broader than just frequency.

It can describe many kinds of increase:

• Ela está cada vez mais feliz. = She is getting happier and happier.
• Eles gastam cada vez mais dinheiro. = They spend more and more money.
• Eu estudo cada vez mais. = I study more and more / more and more often.

In your sentence, context makes it sound like increasing frequency or regularity of checking.

Yes. That is a good translation too.

Cada vez mais often corresponds to:

• more and more
• increasingly

So depending on style, you could translate the sentence as:

• The aquarist checks the pH more and more often.
• The aquarist increasingly checks the pH.

The first sounds more natural in everyday English. The second is a bit more formal or compact.

Yes, in many contexts you can.

• O aquarista checa o pH.
• O aquarista verifica o pH.

Both can mean The aquarist checks the pH.

The difference is mostly register and style:

• verifica sounds a bit more formal, technical, or careful
• checa sounds a bit more informal and is influenced by English check

In scientific, technical, or instructional contexts, verifica is often a very good choice.