Steve-B

Tds 300ppm in tap, I have wicked hard water. Curtly showing same in the tank. Good thought on dechcloring before hand, I'll give that a try. That said, I don't have this problem in other tanks and I have been turning off the canisters and allowing 15 mins to ensure chlorine removal.

Thanks so much for the compliment! Interesting idea on the ammonia. Don't have problems with other filters on smaller tanks, however might be factor with the cannister. Yes they are very nice with the removable pre-filter, a huge plus. Yes there is a separate plug for the heater and the plastic media is k1 like.

I love UV systems. Any thank that is over 100 gallons should have one. In smaller tanks I use them with good results as well. For smaller tanks try using a timer and run for 12 hours, makes the units that don't have a replaceable bulb last longer.

Great thought! I clean the prefilter about once a month. I agree on the chlorine in tap water concern; good insight.

Big thanks to all for the suggestions! Really appriciate the input. The really funny thing about all this is the tank with $30 hang on back, has no problems but the two with $300+ filters do. Here is a link to biomaster if your not familiar...really cool features: https://store.oase-usa.com/products/oase-biomaster-thermo-350 Today I turned off the C02 to all three tanks, 24 hours before my water changes. It is my hope to rule out the ph spike, as this has come to be my lastest thought. The fish come to the top of the tank (12 to 24 hours after water change) which also makes me consider Oxygen depletion, that said I have added air stones in the past but stilll get the same display. Please keep the ideas coming; really appreicate it.

Thanks for the compliments and the thought. I am a believer that few bio medias are bad, truley depend on the system in use. I still have a spounge in the main unit. I have used the cermic media with great success in many cases, especially in sumps.

Good thoughts. Here is a link to the filter. One of the greatest things about this unit it you clean the prefilter and leave the main spounges, ceramic or what every alone. No, I don't clean the innnard at all or maybe once a year. I like to keep a clean tank but not a clean filter ;^) https://store.oase-usa.com/products/oase-biomaster-thermo-350 Thanks for the compliment! I have experimented with 50%, 30%, 20% water changes with these tanks to see if that would be a factor. I tested the tap water but no signifanct nitrate or nitrite. Yes, regrettibly I have lost live stock to the issue, fish show stress by staying at the top of the tank. I have started using a fritz product to bolter the bateria when I see the issue.

Thanks for the question! I did a quick test with a tetra test strip. No significant nitrate or nitrate in my tap water.

Greetings. Thanks to any who might add some insight. I'm new to the forum but rather expericed in the hobby. Six months ago I set up 3 high energy 40 gallon tanks. (high light/C02) I am running Oase biomaster 350 filters on two and a hang on the back on one. (tank on right has the hang on back). All have the same substate, maintance routine and have ceramic media in the filters. After water changes I expericce signifigant nitrite spikes in the two tanks with the cansiter filters. I have removed all but 1 sponge and subbed with more ceramic media. This has increased water flow. I have made these changes over the last 4 months to no avail. It is very clear that beneficial bacteria are dying off during the water changes and I have racked my mind on how to correct. I have not had this problem before and have used one of Oase filters on a 90 gal with no problems. I have tried keeping the fiilters on and turning them off during water changes, but this has not had any effect. I treat for chlorine etc faithfully, tempatures changes occur during water changes but I have no problem with this issue in other tanks. My latest thought is that C02/ph shifts may be the issue. I reallly would appreciate any thoughts. This is a mystry puzzle I am getting tired of playing. Many thanks!