Post cycle water change percentage?    7/3/17
Just a quick cycling question today. I am planning to cycle a saltwater tank using the "phantom feeding method" (ohh, ahh) as I plan t use dry reef saver rock and dry sand. When my cycle has completed, what percent water
change should I do? I have read 100% which seems absurd for larger systems.
The net has conflicting Info and I could not find this anywhere on cycling marine systems pages 1-9. Thanks.
<I agree with your apparent caution here. I would change about a quarter/25% of the water out, wait a week, and then another quarter.
Post-cycle times can be a bit tricky, and one does not want to cause a metabolic check, or nitrifier die-off via too much change too soon. Bob Fenner>

cycling of saltwater aquarium; RO malfunction          4/7/15
Hi,
I’ve cycled many tanks over the years but have never dealt with this particular issue before. I live in an agriculture state now ,but was a recent move. I have an ro filter hook-up for drinking water which I used to fill the tank after taking a sample to PetCo for them to test the water .I did not have testing kits yet. I was told all was well ,
<Mmmm>
so I went ahead and filled the tank, and began a fishless cycle. I added ammonium chloride to the tank, waited a few days to test with my new SeaChem test kits. I did not initially get a free ammonia level, but did get a total ammonia level of 0.5- 1.0. It’s hard to decipher the gradual color changes. Even though I figured it was too early to get any reading from nitrite, nitrate testing
<For browsers and you; I WOULD be adding some other "feeder stock"; likely at least a proteinaceous food AND a bacteria culture of use>
I did that along with ph and alkalinity testing. I was surprised to find the water testing positive for both nitrite and nitrate at 2 and 20ppm respectively so soon.
<Mmmm; again... some other source>
Long story short there is both the same numbers in the ro filtered water
<?! Should NOT be coming through an operating RO device>
I had coming from the tap. Now I have to try to figure out is this tank cycled once the total ammonia and nitrite levels go to zero?
<Should be>
It’s a 90 gallon tank and I’d hate to drain it and refill so I plan to use a product called az-no3
<A real product. I.e.; it works>
to get rid of excess nitrate that’s in the tank after cycle and before any thing living goes in and the get ro/di unit to do water changes from then forward.
<I'd look into adding at least an activated carbon contactor module to your string... that is, another step in your Reverse Osmosis tool>
Right now I’m getting sporadic free ammonia readings (sometimes 0.2 or so , sometimes zero) and a consistent total ammonia reading of 0.5 every few days when I test. Nitrite and nitrate still holding about the same at above mentioned numbers and I’m about 1 1/2 weeks into the cycle (which is still way early, I know and understand that). I just wondered if there is going to be a drop in the nitrite since it’s not being converted but pre-existing in the water?
<A few things else may be going on here... the source, type of nitrogenous (and other) compounds in your source water that are evidently getting past your RO... I really just urge what has been stated above. The addition of flake or pelleted food likely; AND a real aquarium-beneficial mix of microbes; ala Dr. Tim's, Microbe-Lift, SeaChem...>
I’m sorry if this seems like a silly question ( I’m not the best with chemistry) and wanted a second opinion on what to expect.
<Not silly; actually profound>
90 gal. corner bow
Aquamax cones protein skimmer HOB
Hydor 600 canister filter
2 Hydor powerheads for circulation
instant ocean reef crystals as salt mix
3 inch sand bed
no rock as of yet (plan to get life rock once cycled, has bacteria in it from what I gather)
<Oh! The rock can sub for both the food and bacterial additions... just a few lb.s>
Thanks Gail
<Welcome; Bob Fenner>
Re: cycling of saltwater aquarium          4/7/15
Hi Mr. Fenner,
Thank you for your quick reply and I have solved the mystery of the faulty water!
<Oh?>
After receiving your email last night I decided to test the regular tap (unfiltered) and there were no nitrites and maybe 1ppm nitrate in that water, so I have to conclude that my filter was installed incorrectly or backwards!
<Ahh>
If I hadn't decided to start up a tank and had not contacted you it may have been quite awhile till I noticed anything amiss. I will now contact the company and find out how to fix this mess along with the handyman who installed it and give him a piece of it. I may also have to drain tank after all if anything worse that nitrite and nitrate got flushed into that water.
<I'd just wait at this point... the little bit in there presently is of little consequence>
If they give me a breakdown of the chemical composition of the water and I'm not sure if it should stay or go I
may call upon your expertise to say yea or nay, if that's ok with you.
<Sure>
For right now until I have the facts everything will be in stasis. Thank you for possibly saving mine and my family's life, we are so very grateful you do what you do!
Thank you, Gail
<Very glad to be of assistance. Bob Fenner>