Если не считать водорослей, налёт уже убрали.

Yes, literally если не считать means something like if not to count or if we don’t count. But in real usage, this whole expression often works idiomatically as:

• except for
• not counting
• aside from

So in this sentence, Если не считать водорослей is not really a logical condition in the ordinary if... then... sense. It is more like an introductory phrase meaning except for the algae.

A very close English equivalent would be:

• Except for the algae, ...
• If you don’t count the algae, ...

Russian often uses если не считать + genitive this way.

Because the expression не считать in this meaning commonly takes the genitive.

So:

• если не считать водорослей = if you don’t count / except for the algae

Here водорослей is the genitive plural form of водоросли.

This is something learners often just need to remember as part of the fixed expression:

• не считая + genitive
• если не считать + genitive

So the case is not random; it belongs to the construction.

The dictionary form is водоросли.

That is a plural noun meaning algae or seaweed, depending on context. In this sentence, the form changes to водорослей, which is the genitive plural.

So:

• nominative plural: водоросли
• genitive plural: водорослей

This is why you do not see водоросли in the sentence.

Because Если не считать водорослей is an introductory clause/phrase before the main clause.

The sentence has two parts:

• Если не считать водорослей,
• налёт уже убрали.

Russian normally separates this kind of opening phrase with a comma, especially when it begins with если and introduces the main statement.

So the comma helps show:

• first, the exception-setting phrase
• then, the main information

It is the object of убрали. The reason the form looks unchanged is that налёт is:

• masculine
• singular
• inanimate

For masculine inanimate nouns, the accusative singular is the same as the nominative singular.

So:

• nominative: налёт
• accusative: налёт

That is why the direct object appears in the same form as the dictionary form.

This is a very common Russian pattern. Убрали is past tense, plural, perfective, and it literally means they removed / they cleaned up.

But Russian often uses 3rd person plural with no stated subject when the doer is:

• unknown
• unimportant
• obvious from context
• meant in a general they sense

So налёт уже убрали can mean:

• They’ve already removed the deposit/coating
• The deposit has already been removed

English often prefers the passive here, but Russian very often uses this active plural form instead of a passive.

Because убрали is perfective, and perfective aspect focuses on a completed result.

Here the idea is that the action is already finished:

• already removed
• already cleaned off

So убрали fits well with уже.

Compare:

• убрали = removed, finished removing
• убирали = were removing / used to remove / removed in process, with emphasis on process or repetition rather than the final result

Since the sentence is about the completed outcome, perfective убрали is the natural choice.

Уже means already.

It tells you that the action happened before the present reference point. So:

• налёт убрали = the deposit was removed
• налёт уже убрали = the deposit has already been removed

It often gives the sentence a sense of this has been done by now.

Yes, налёт is a common word, but its exact meaning depends a lot on context. It can refer to a thin layer or deposit on a surface, for example:

• plaque on teeth
• a coating or film
• residue
• buildup
• tarnish-like deposit

So in different contexts, English translations may vary. Russian uses налёт fairly broadly for something that has formed as a layer on a surface.

Yes, that would be possible in many contexts.

• Если не считать водорослей, ...
• Не считая водорослей, ...

Both can mean except for the algae or not counting the algae.

The version with если can sound a little more like if we set aside / if we don’t count. The version without если is often more directly excluding / not counting.

In many real situations, the difference is small.

Russian word order is flexible, and different orders shift emphasis.

• Налёт уже убрали puts налёт early, so it sounds like as for the deposit, that has already been removed
• Уже убрали налёт puts more focus on the action removed already
• Налёт убрали уже is also possible in some contexts, often with a different intonation

So the chosen order is natural and helps present налёт as the topic before giving the new information that it has already been removed.

Grammatically, it is active, because the verb is убрали = they removed.

But functionally, it often corresponds to an English passive:

• Russian: Налёт уже убрали
• English: The deposit has already been removed

This is a very important pattern in Russian: an active verb in 3rd person plural can be used where English might prefer a passive construction.