Nitrate problem in fresh salt water

wlninja

wlninja

Member
I have been having issues with Nitrates and tonight I think I found part of the problem. I did a nitrate test on my tank and was at 30 after a 30% water change. Then I did a nitrate test on my RO/DI water and it is 0. I did a test on 1/2 a gallon of fresh 1.025 salt water I made specifically to check nitrates (I use Instant Ocean salt) and got 0. I did a test on some left over water from today that's still in my mixing trash can (32 gallon brute trash can that was bought brand new specifically for salt water mixing) and my nitrates are 15. I just mixed the salt water today after letting the can fill up yesterday. I have no idea how I'm getting nitrates in my fresh salt water. Here is my process:


Run 100 watt heater in trash can at 76 degrees so water is same temp as display tank.
Run Aquaclear 40 power head in the bottom of the can for water movement.

Rinse heater, power head, and trash can then dry.

Fill trash can to approximately 25-28 gallons.
Once the can is filled to my mark I then begin adding salt. I add 10 cups of instant ocean (1/2 cup per gallon) and let it sit until it dissolves. Then I check salinity with a refractometer and add more salt accordingly. Once the salinity is correct I usually do the water change within a few hours.

Ive been noticing brown residue lately when cleaning the trash can out so I have been rinsing it and wiping it dry then letting it sit for a couple days before starting the RO/DI process.

Also I keep the lid on my can during the entire process so very little if any light is getting in.

Any idea what may be happening?

Thanks!
 
JWarren

JWarren

Active Member
First question; what is the nitrate level of the water you are rinsing the trash can out with?

Second question; have you tried letting your salt water mix for 24 hours and induce air?

Third question; are you letting the can air dry or are you drying it out with a towel that has been washed?

The water you rinse the can with and any towels could be a source of cross contamination. The water, if it contains high levels of nitrates, could leave enough residue on the surface of the can to give you a reading. A towel could contain nitrates from the soap or any fabric softeners it is washed in as well as the water.

Add air to the water to drive of any excess CO2 and check for nitrates again. A powerhead like the Rio's will induce quite a bit of air into the water and is real good for this purpose. An air stone will also work well near your mixing pumps intake. so it sucks in a few bubbles at a time.

Always a good idea to get a second opinion by taking samples of all your water to your LFS and have them check it as a comparison against your tests. It is always possible to get a bad test kit.
 
wlninja

wlninja

Member
I use paper towels to wipe the can out with sometimes and other times I just let it air dry.

Im using regular tap water to rinse the can with. Ill do test on my tap water tonight.

I will try adding an air stone to the can later this week when I make a new batch (waiting on new carbon filter and sediment filter for my RO unit).

Thanks for the info!
 
JWarren

JWarren

Active Member
When trouble shooting a source of something like nitrates, everything has to be suspect. You are not the first to complain of unexplained nitrates in relation to IO, as I am one of those that have found nitrates coming from the salt mix when everything else checked out OK and I have been an IO fan for almost twenty years.

Do you have a DI filter as well? Have you checked your TDS and phosphates? If you have either coming in with your filtered water, then you have the possibility of nitrates coming in as well.
 
wlninja

wlninja

Member
Have not checked TDS yet. I have a meter on order and it should be arriving tomorrow with my replacement filters for the RO unit.

I have a 4 stage RO/DI unit so I am using DI water. I will do a full water test on my RO water tonight and see if I have any other abnormal levels coming out of my unit. And tomorrow (when the meter arrives) Ill do a test for TDS on both source and RO water.

Thanks again for the advice!
 
wlninja

wlninja

Member
Ok This evening after I got home I ran some more tests.

Tap water nitrate level 80! No more rinsing equipment with tap water!

I let a couple flakes of fish food sit in a 60 mil beaker of RO water (no salt added) since last night and tested the nitrate level tonight and I got about 5-10 on that test, however that is a very concentrated amount of fish food for 60 mils of water, still having nitrates show up on the test makes me wonder if I should switch out food as well?

Emptied and dried out my mixing can. Then I used RO water in a wash bottle to wet down a small area on the bottom of my trash can. I then used a 5mil pipette to suck up the water and do a nitrate test on. It came out zero leading me to believe that if rinse my entire can with ro water then dry it that should help.

I should be getting my new filters and TDS meter tomorrow so I plan to rinse the can out then let it sit empty for a day and then make another batch of Salt and see what happens.
 
JWarren

JWarren

Active Member
I'm interested to see what the TDS of the tap turns out to be. :)

My tap nitrates are at 65 here in Florida and that is city water. My TDS is 350; legal limit is 400ppm.

Won't catch me drinking it! :)
 
wlninja

wlninja

Member
Well I got my new parts today and the new pH/TDS meter. I have pH calibration fluid but completely forgot to get any TDS calibration solution. Not sure how out of wack the unit might be from shipping but I tested both Tap and RO water tonight.

RO was water still in the first 10 gallons after I replaced the pre-filter and carbon block. 4ppm

Tap water was 104ppm.

Course my meter could be out of wack too. I'll have to check and see if we have any calibration solution at work (We have two labs with pH/Conductivity bench meters so they should have something).

I am concerned that my DI canister is shot and my membrane may be failing. My water production seems to be a good bit less than usual after installing the new filters. Also the DI canister it looks like the bottom of the crystals inside the canister have broken off and are separating from the rest. I'm not exactly sure how to explain it better and my camera is MIA at the moment. Kind of stinks too because I just ordered the filters and if I had known I could have gotten everything at once. :-/

The other weird thing with my RO unit is the DI canister is not filled up completely with water. Earlier today it was running maybe 1/3 full of water. Its now filled back up to about 80% full but I don't remember it ever running for an extended period of time and not being full. Anyone think I need to replace it and/or my membrane?

Forgot to mention I'm on city water.

Just tested the RO water again. Put about 60 mils into a clean plastic beaker from right out of the unit and got a reading of 0ppm.

Thanks!
 
wlninja

wlninja

Member
After replacing the Pre-filter and carbon block in my RO unit I have been making batch after batch of saltwater all coming out with 0 nitrates. The only other thing I am doing differently now than I was before is pumping air through the water for 24 hours before testing/using the water.

I have an airline connected to the power head I use to circulate the water in my can and also I use an air stone.

Ever since I've started doing this I've had perfect quality water. Thanks to everyone that chimed in!
 
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