# HYDROS App vs ReefATLAS PAR Estimator

The clearest difference is rating: ReefATLAS PAR Estimator at 5.0 against HYDROS App's 3.6. ReefATLAS PAR Estimator also leads on update cadence (daily vs every 3 months). HYDROS App's advantage is in-app purchases (none vs 1) and ratings volume (23 vs 1). On price, ads, device support and iOS requirement there is nothing between them.

Both are free to download. ReefATLAS PAR Estimator sells 1 in-app purchase, starting at $4.99 per month. HYDROS App asks for nothing beyond the download.

ReefATLAS PAR Estimator holds the better App Store score, 5.0 against 3.6. That said, the two scores are not equally well evidenced: HYDROS App has 23 ratings behind it against 1, so its average is the more settled of the two.

HYDROS App ships an update every 3 months, ReefATLAS PAR Estimator daily. The most recent releases landed on October 22, 2026 and October 19, 2026 respectively.

## The numbers

| Metric | HYDROS App | ReefATLAS PAR Estimator |
| --- | --- | --- |
| Price | Free | Free |
| Rating | [3.6 (23 ratings)](https://appshunter.io/ios/app/hydros-app/id1455344294/reviews) | **[5.0 (1 ratings)](https://appshunter.io/ios/app/reefatlas-par-estimator/id6777574663/reviews)** |
| Number of ratings | **23** | 1 |
| Positive reviews | 62.3% of reviews | — |
| In-app purchases | **No** | Yes |
| Ads | No | No |
| Update frequency | Every 3 months | **Daily** |
| Monetization | **Free** | Subscription |
| Size | 70 MB | 27 MB |
| Requires iOS | 15.6 | **14.0** |
| Devices | iPhone, iPad, iPod | iPhone, iPad, iPod |
| Age rating | 4+ | 4+ |
| Developer | [Coralvue](https://appshunter.io/developer/1455344293) | [JONATHAN ALBERT PITTMAN](https://appshunter.io/developer/6777574665) |

## What reviewers say

### HYDROS App

[App page](https://appshunter.io/ios/app/hydros-app/id1455344294)

Easily monitor and control your aquarium's vital parameters like temperature, pH, and salinity. Manage all your connected devices, including ATOs, lights, and pumps, with a user-friendly interface. Quick setup with preset configurations means no coding is required to get your system running.

**Highlights:** Monitor temperature, ORP, pH, salinity, Control ATO, lights, heaters, pumps, User-friendly interface, Quick setup with presets, Manage multiple devices and aquariums, Set schedules and create modes

**Features:** macOS Compatibility, Vision Pro support

**In-app purchases:** none


### ReefATLAS PAR Estimator

[App page](https://appshunter.io/ios/app/reefatlas-par-estimator/id6777574663)

This app helps reef aquarium enthusiasts estimate and visualize light distribution without a PAR meter. It allows users to input tank dimensions, lighting equipment, and water conditions to predict PAR levels and make informed decisions about coral placement and lighting setups. The tool offers interactive 3D visualizations and supports a wide range of popular reef lighting systems.

**Highlights:** Interactive 3D PAR heatmap visualization, Support for popular reef aquarium lighting systems, Multi-fixture light array setup, Fixture placement and angle controls, Spectrum and intensity adjustment tools, Custom tank dimension configuration, Surface agitation and lid modeling

**Features:** macOS Compatibility

**In-app purchases (1)**

| Purchase | Price | Billing |
| --- | --- | --- |
| ReefATLAS PAR Estimator Monthly | $4.99 | per month |


## Frequently asked questions

### Is HYDROS App free?

HYDROS App is free to download, with no in-app purchases.

### Is ReefATLAS PAR Estimator free?

ReefATLAS PAR Estimator is free to download, with in-app purchases available.

### Which has better reviews, HYDROS App or ReefATLAS PAR Estimator?

ReefATLAS PAR Estimator is rated higher. HYDROS App averages 3.6 out of 5 from 23 ratings, while ReefATLAS PAR Estimator averages 5.0 from 1 ratings.

### Do HYDROS App or ReefATLAS PAR Estimator have ads?

Neither HYDROS App nor ReefATLAS PAR Estimator shows ads.

### Which is updated more often, HYDROS App or ReefATLAS PAR Estimator?

HYDROS App ships an update every 3 months, and ReefATLAS PAR Estimator daily. Most recently, HYDROS App was updated on October 22, 2026 and ReefATLAS PAR Estimator on October 19, 2026.

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*Compared by [AppsHunter](https://appshunter.io/) from daily US App Store data. Review summaries are generated from verbatim App Store reviews.*