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Tusa Zen IQ-900 - Multifunctional Dive Watch Computer With Dynamic Personality

Tusa Zen IQ-900 - Multifunctional Dive Watch Computer With Dynamic Personality

Even though Tusa ZEN IQ-900 has advanced features and functions that may be welcomed by advanced divers and guys who do freediving, it may be recommended dive computer for the beginners in diving as well. 2 Nitrox mixes, 4 dive modes, plenty of features in one compact package!

General Information
User Interface
Your Review



Tusa Zen IQ–900 is made in a classic dive watch computer style. It has 4 dive modes and fully functional digital watch, so you may use it not only underwater but also wear Zen onshore. Even though it has advanced features and functions that may be welcomed by advanced divers and guys who do freediving, this dive computer can be used successfully by the beginners in diving activities as well.

In July 2010 Tusa released a firmware update to fix some glitches and improve performance of Tusa Zen IQ–900 dive computer. This update can be downloaded from Tusa website.


Tusa ZEN IQ-900 Features Card

Copy this Tusa ZEN IQ-900 Key Features & Alarms Card for your Reference and Share with your friends and buddies!


Above mentioned alarms are for Air and Nitrox dive modes, FREEdiving mode has its own alarms and we will discuss them later in following sections.



Benefits of using Tusa ZEN IQ-900 dive computer

  • you will be diving with an advanced dive computer that will help you growing in your diving career;
  • you will get instrument that has high level of customization;
  • you will be ready to enter technical diving with the help of Tusa ZEN IQ-900 dive computer;
  • you will be able to replace battery yourself and with data retention keep all settings safe;
  • you will have the instrument that works well underwater as dive computer and in office or restaurant as a digital wrist watch








User Interface
4 buttons
Dive Modes
Air, Nitrox, Gauge, FREEdive
Standalone Digital Watch
Buhlmann ZHL – 16C
Number of Gas Mixes
Mix 1 – Air, 21% - 50%;  Mix 2 – Air, 21% - 100%
1.2 - 1.6 ATA
Air Integration
Safety Stop (SS)
Deep Stop (DS)
Conservative Factor
Altitude adjustment
Gas Switching
Dive Planner
9 - 57 meters
Logbook Capacity
24 most recent dives
Max Operational Depth
100 meters
Backlight duration
0/5/10 sec
Sampling Rate
2/15/30/60 sec
User Replaceable Battery
Data Retention
PC Interface
2 years










Tusa Zen IQ-900 has 4 control buttons on user interface and 3 bar graphs for graphical representation nitrogen loading, ascent speed, and oxygen toxicity. These bar graphs will be familiar to you if you used before dive computers from Aeris or Oceanic. If you didn’t – no problems, it easy to interpret their meaning. Brief descriptions each of them you may find below:

  1. Nitrogen Loading Bar Graph (NiBG) – shows nitrogen level during dive and after. When diver goes deeper and stays longer his/her nitrogen level increases and Zen adds new segments to this bar graph, and when person ascends or performs decompression – nitrogen level decreases and dive computer takes away segments; full bar – Decompression mode;
  2. Oxygen Level Bar Graph (O2BG) – shows oxygen toxicity level if Zen set for Nitrox, because there is a different ratio of oxygen in nitrox mix and diver’s body responds differently to this – it this case person may have risk of oxygen toxicity. It works the same as a NiBG – adds and subtracts segments; full bar – High O2 alarm;
  3. Ascent Rate Indicator (ASC) – this one works as a speedometer – displays speed of diver’s ascent by showing certain number of segments; full bar – message SLOW and audio


Display has main and alternative screens, so you need to press ADVANCE button to move between them to view additional dive data.

I may say that buttons are quite big and easy to press, digits are big too – no problems for viewing and backlight is strong enough – so there should not be any troubles during diving with Tusa Zen IQ-900.







All adjustable functions are divided to certain groups and will be familiar to you if you used Oceanic dive computers before.


Tusa ZEN IQ-900 Settings Card

Copy this Tusa ZEN IQ-900 Fine-Tuning Card for your Reference and Share with your friends and buddies!


It is useful and convenient to plan repetitive dives and Tusa Zen IQ–900 has a special function for this – Plan Mode. Using this mode you may see calculated No-Decompression Times for your next dive, according to nitrogen and oxygen toxicity levels from your previous dives (if any).







Setting water activation to ON before diving and Tusa Zen IQ-900 will activate dive mode when it senses depth of 1.5 meters.


Tusa Zen IQ-900: Diving With Air & Nitrox


Tusa ZEN IQ-900 NO-DECO Card

Copy this Tusa ZEN IQ-900 No-Decompression Displays Card for your Reference and Share with your friends and buddies!


During No-Decompression dive Tusa Zen IQ-900 may give us Deep and Safety stops prompts upon reaching certain conditions. There is no any penalty applied if we miss Deep and Safety stops, because they are recommended and not compulsory. But it is a good idea to complete them just to be on the safe side!

It is worth to say about upgrade from Tusa here. Safety Stop prompt used to show depth of 4.5 meters before, but now with new upgrade Safety Stop depth will be 5 meters.


As this dive computer allows using 2 Nitrox gas mixes, we may swap mixes during a dive, of course, if we enabled 2nd gas mix. It is easy procedure, and if you want to change to gas mix with higher PO2 than allowed – Tusa Zen IQ-900 will warn you by giving audio alarm and displaying certain message.


Tusa Zen IQ-900 activates Decompression mode, if we exceed our No-Decompression Limits (NDLs). Upon entry into this mode you will hear an audio and applicable dive data will be displayed. From this moment all calculations will be made regarding to Decompression mode. Following information will be displayed:

  • bar graphs: NiBG, O2BG (if applicable);
  • Total Ascent Time (TAT) – time required to reach surface safely;
  • Stop Depth and Stop Time;
  • current depth;
  • cylinder icon of gas in use;
  • max depth reached during a dive;
  • time;
  • temperature, etc.


Decompression display has main and alternative screens and above is a summary of what we get. To move around displays – use ADVANCE button.

During decompression, diver may create, so called violations, which happen if he/she ascends shallower and stays for some time above the displayed decompression stop depth, or diver may descend deeper than Maximum Operational Depth (MOD), or decompression requires ceiling depth range between 18 m and 21 m deep.
In this case scenario Tusa Zen IQ-900 activates appropriate Violation mode and manages it to help us safely perform decompression in those situations.


Tusa Zen IQ-900: Diving In GAUGE Mode

Next Dive mode of Tusa Zen IQ–900 is Gauge. Dive computer doesn’t perform any calculations of nitrogen and oxygen loading and decompression condition. It can be used as a depth gauge and timer only. As with other dive computers, after diving with this one in Gauge mode, you need to wait 24 hours before you may use it for diving with Air or Nitrox.

Display shows dive data similar to listed below and it is a summary from main and alternative displays:

  • current and maximum depth;
  • time and temperature;
  • Elapsed Dive Time (EDT);
  • ASC (if ascending)


Tusa Zen IQ-900: FREEdiving

Other Dive mode of Tusa Zen IQ-900 is FREEdiving. People who do freediving may be particularly interested in this one, because it has set of functions that may satisfy well this sort of diving activity!

Along with its own functions, Freedive mode shares some settings with Air and Nitrox dive modes, like time and date, Personal Conservative Factor settings and backlight duration.

Dive computer calculates nitrogen loading according to Air by default and the residual amount that you may have left between diving with Air, Nitrox and this freediving.

Special settings and alarms for freediving can be accessed and set from Free Surface mode. We may set following functions and alarms:

  1. Free Countdown Timer;
  2. Freedive Elapsed Dive Time (EDT) alarm – ON/OFF, factory preset to 30 seconds and can not be changed;
  3. Freedive Depth alarms – 3 depth alarms that can be set at progressively deeper depths at a range 10 – 100 meters in 1 meter increments


During freediving display shows following dive data (summary from main and alternative displays):

  • NiBG (if you have any level of residual nitrogen from previous dives);
  • No-Decompression (NDC) Time Remaining;
  • Elapsed Dive Time (EDT);
  • current and maximum depth during a dive;
  • time and temperature;
  • Countdown Timer (CDT) status


And that’s for sure – you will meet freediving alarms that you set before – Dive Time alarm and Free Depth alarms with all appropriate data displayed and stored in on-unit memory for further downloading to PC.

There is another type of Freedive alarm – Free NiBG alarm. This one activates when nitrogen remained from previous dives and current nitrogen loading hits the Caution zone. It may even happen when nitrogen level will increase to Decompression condition.
In this scenario Tusa Zen IQ-900 will activate Violation Gauge Mode (VGM) for 24 hours, which means that diver must stay on surface for 24 hours without any diving activities.


Freedive data can not be displayed by this dive computer – you need to buy optional PC interface cable and download software from Tusa website to view and organize freedive data on your PC.

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After we went through all dive modes of this dive computer – it is time to review our Logs, History, download data to PC (who has interface, of course!), or maybe plan subsequent dives.

Below is a summary of Tusa Zen IQ-900 functions that may be accessed on surface after the Transition period (10 minutes after the dive):

  1. Plan mode – this function allows us to plan next dives for Air and Nitrox and calculates our No-Decompression (NDC) times according to residual nitrogen and oxygen remaining from previous dives; it works only with 1st gas mix, even if 2nd gas mix was enabled – it doesn’t make any effect on calculations; it shows us available times for depth at range 9 – 57 meters;
  2. No-Fly Time Counter;
  3. Desaturation Counter;
  4. Logbook mode for Air, Nitrox and Gauge – shows information about the most recent 24 dives and has 2 pages of extensive dive data;
  5. History mode – stores dive data of 999 Air, Nitrox and Gauge dives, 9999 dive hours, and maximum depth reached. For Freedive History and Logs we need to have PC interface cable to transfer freedive data to computer for viewing and organizing;
  6. PC upload and download dive data (with optional PC interface cable)







Tusa Zen IQ-900: What Divers Say


  • easy to set and easy to use dive computer, good as a watch too;
  • this dive computer is everything you need for recreational diving, once you figure out manual everything is clear;
  • smooth gas switching operation;
  • recommended dive computer for the beginners and recreational divers



  • may have internal firmware glitches;
  • manual could be better


I reckon Tusa designed and produced pretty decent dive computer that can compete in nowadays scubadiving market and win!

Though it is very similar to some Oceanic models – it still has its own personality and distinctive features, like large digits that are easy to read underwater; dual nitrox gas mix; automatic altitude setting; data retention function and some others.

We didn’t have and didn't notice any troubles while diving with Tusa Zen IQ-900 dive computer. Buttons were easy to press and display was clearly readable. All decompression and conditional violation data was managed smoothly as well.

From the specs, features and price point of view I think Tusa Zen IQ–900 can be definitely a winner!


Tusa ZEN IQ-900 dive computer
Tusa ZEN IQ-900

Dive-Computer-Wizard Rating
golden star golden star golden star golden star silver star


So if you need multifunctional dive computer with 4 dive modes, 2 Nitrox gas mixes, and want to save money for your other scuba diving equipment – you definitely need to invest into Tusa Zen IQ–900!



Add comment
Chad, 22 November 2013 10:04
All-Round & Stylish Dive Watch Computer

We are doing great with Tusa Zen. This is similar to older dive computers made by Aeris and Oceanic with Haldanean algorithm.

I use Tusa Zen at its full capacity - two gas mixes and all dive modes. It is easy to program and 4-buttons interface not difficult to learn and get used to.

Surely, I had sometime to become familiar with all operations.

I can wear it as a wrist watch as Tusa Zen has full wrist watch functions with dual time, alarm clock, and chronograph. Display is large and well-structured. I don't have troubles to interpret of what is shown on it. Even smallest digits are sharp and clear.

PC connection is reasonably well. And battery replacement can be done by diver with data retention, which is very convenient if I'm travelling.

Lisa, 5 October 2012 03:38
I Am Very Confident To Go Underwater With My Tusa Zen IQ-900!

I always wanted to have something special that emphasize my personality and I found that Tusa Zen was everything I wanted! I may wear this computer as a normal everyday watch, but I don't use this option - it is a little bit big for a lady, but underwater Tusa Zen gives me possibility not only use it with dual Nitrox mix, but also for freediving! It is an advanced dive computer and it is very elegant.

It has loud alarms and display has good contrast, so I am always sure that I won't miss anything important. Bar graphs are very informative too. Very easy to switch gas mixes. It is, actually, easy to use dive computer after I got few times through the documentation.

Also I like Personal correction factor setting for extra-safety and deep and safety stops options. Tusa Zen measures and compensates altitude automatically - so I don't need to worry about that!

User replaceable battery with battery "hot swap" - that's very convenient as well, as I can swap the battery just on the boat - no need to send it to service center!

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