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Coral Reef Tank Water Basics

RODI Water Filter


Coral are a wonderful and beautiful exotic animal. Care and requirements vary from specimen to specimen but most have the same basic needs. Water parameters are very important to get right from the beginning. In addition to good water parameters, you will need proper water temperature and reliable flow.

Water parameters can be fairly easy to get right with practice and the proper equipment. In general, I always recommend using an RODI water filter. For most people, a standard 4 stage RODI system will be plenty. In some cases it may be required to add additional stages if the water has harsher chemicals. The goal of using a RODI filter is to bring TDS down to 0. If it is higher than 0 then there is still stuff in the water that can harm the coral or lead to unwanted issues such as algae blooms. Once the water has been filtered and TDS is 0 you can begin adding in a reef tank salt mix. If you choose a trusted reef tank brand salt mix, the salt mix adds back minerals and nutrients in the proper ratio if you bring it to the proper salinity. Once the salt has been mixed completely you should bring it to the proper temperature for the reef tank. As coral grow they will absorb the nutrients from the water. This will cause the water parameters to slowly change over time. To fix this, it is recommended to do a 10-20% water change every other week. Remember to top off any evaporated water with FRESH water.

Temperature is the easiest care requirement to meet. Most coral in the reef tank hobby are tropical and prefer water temperatures between 76-82 degrees F, with a sweet spot between 78 and 80 degrees F. Most aquarium heaters will be able to get water to this temperature and keep it stable.

Flow is another easy care to meet, but it requires a little more work. It is heavily dependent on the type of coral and other things such as rock work and tank size. In the reef tank hobby we have a general guideline of 10x tank turnover per hour. So a 50 gallon tank should have about 500 GPH flow. To keep it simple, most aquarium pumps will be rated for a certain tank size. You will need to make sure you do not have any dead spots (really low flow parts of the tank) due to rock work. You will also want to make sure the pump is not directly flowing onto a coral. Most prefer indirect flow. More advanced options are to include a wave maker to simulate its natural environment. Some of the newer (more expensive) pumps have settings to mimic this.

TDS Meter



I just wanted to add a little disclaimer.

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There are a lot of ways to get something done in this hobby. While I talk a lot about RODI water and filters, it is not the only way to keep coral. Some people struggle to transport large volumes of water (understandable) or they do not have the space to keep the filtration equipment AND water supply.

I know of some people that buy gallons of "purified" water from the grocery store to make saltwater or top off. These are normally for smaller apartment or office tanks though. I have looked into this before and decided against it. Normally the TDS meter will read between 5-25 when I want it to read 0. Your mileage may vary though.

This is something to research and consider if you are struggling to make your own water. I personally do not like these other methods because it takes control away and leaves things up to chance. If I am spending a lot of hours and money to keep an animal healthy I would prefer to be as careful as possible.

Remember, you can also buy boxes of pre mixed saltwater from most pet stores. I think this is a better option for smaller tanks if an RODI filter is not realistic. A lot of specialty fish stores will also sell fresh RODI water for a fair price. This can be hard for some people because now you need to drive the water back to the tank.

This content reflects the personal opinions of the author. It is accurate and true to the best of the author’s knowledge and should not be substituted for impartial fact or advice in legal, political, or personal matters.

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