i am cycling a new 75 gallon tank with oscar and pleco in tank[i know, big no no,but thats how it had to be the old 10 gallon was too small!!!] any way when i take more than about 22.5 gallons out during water changes my hob filter system suks air and does'nt cycle water is this ok? or should i just turn it off and do a bigger water change? yesterday my levels were ammonia 1.0,nitrite 1.0,nitrate 10, ph 7.6. did a 25 gallon water change and today the levels are almost exactly the same except for nitrate which went down to 5.0. this is day 12 of the cycle.

you should have started filling the tank gradually based on the small tank.
if you just transfer all stuff from the 10 gal tank, fill a little more water
until the filter is submerge enough to run and turn over the water... you should
be fine. adding water the following day equivalent half of the existing is the
best thing to do without discharging any water...then add again the following
day another equivalent half and go on until the tank is filled to the capacity.....

the principle here is that instead of removing the water, you just add as if
you are changing water...beneficial bacteria will remain and multiply...when
you reach the full capacity, the system is cycled and your fish should be fine.

ok, here is what you need to do. If you already do this than thats great!

Turn of heaters and filters when changing water. Two reasons! 1. obviously it sucks air! 2. When you change water, you are adding chlorine filled water, or chloramine depends on where you live and this kills any good bacteria you may have, which wont be very much.

Use PRIME water conditioner, ( i have tested several brands this is the only one that brought my tap water down below .25 within 10 minutes from a bucket test. if you have high levels in your tap of chloramine, then double your dose of conditioner. The reason Prime is so good is it breaks up the highyl stable compound of chloramine much better that the competitors) have the filters turned off, and vacuum your gravel. Slowly fill the tank back up with water and be sure to add the PRIME first to the aquarium. After you have filled the tank, let it sit for about 10 mnutes or so and be sure to have some bubblers on for oxygen and some circulation. This will give the water enough time to get low enough to turn the filters back on which once you have the tank fully cycled shuld control the remaing chloramine ammonia whatever...

large water changes are the key to getting ammonia down. You need to be doing bigger that 22 gallons. You need to do at least half if not more. Dont worry, a large amount of any beneficial bacteria is not going to be in the water anyhow, it should be in your media, as gravel is only static and is only good once something comes into contact with it.

Speaking of filtration. You say you have HOBs. What kind are you running on a 75 gallon? You need at least 5 times the volume of the tank in terms of flow rate for a canister, and 10 times for HOB. This is for Oscars and other messy cichlids. So your filters should be pushing a minimum of 750 GPH in a 75 gallon tank (75gal x 10 =750 GPH of for canister 75 gal x 5 = 375 gph)

I hope you do not use carbon filtration. Carbon is not needed and bio and mechanical is all you need for a great biological cycle. The more bio media, the more places for good bacteria to grow and control high levels of ammonia and nitrites.

In a HOB what I used to do and still do since I have 2 hobs with 2 canisters on my tank, is to slit the top of the carbon bag, empty carbon out, stuff tightly wil ceramic rings or someother bio media that you get from the LFS. The pad in front of it shuld be facing the water output and this is a fiber/spongelike substance that polishes water and grabs more debris.

Good thing about bio media is it can be rinsed with tank water and put back in, no need to replace the cartidge every month like with carbon!

daily water changes until readings (ammonia and nitrite) are below .25ppm are necessary. Adding bio media is the first thing you need to do or you will have an never ending bacterial bloom.

You have a slow start on nitrates, and it will guarantee to imporve quicker with bio media. your tank is fully cycled but I think your fitration is not sufficient to handle the load. That is why you are having spikes. If this makes sense than good, if not please ask for clarification and I will do my best to help you get through this as ammonia is very toxic.

Are they eating and active??

Need to get this down asap, this harms internal organs..

It sounds like your in a pretty tough spot. Just keep doing daily 25-30 pct water changes. Once you get 20+ppm Nitrate level, then just test daily and if you get any ammonia or nitrite at all do a water change. You could also use some chem to speed up the process I would suggest API STRESS ZYME. Just add 5 ml per 10 Gal of water you change (directions are also on the bottle).

mylutino Im pretty sure tyour required GPH is way off. By your numbers a EHEIM Pro III 2080 would not be enough for a 100 Gal tank.

yeah thats gonna help immensly! yes they are very active and would eat me outta house and home if i would allow it. as for my hob filter its a marineland emperor 400 it says it filters 400 gallons per hour. i'll try the larger water change tonight. i've been only changing out 25 to 30 gallons at a time i'll try 50 percent.thanks alot!!

thanks yeah i am using the stress zyme also.

I would be careful doing water changes that large. Really a water change that big should only be for emergencies. 30 pct water changes daily should keep your tank fairly healthy till the cycle kicks in. If you do want to do a 50 pct watre change be sure you have digital thermometer and get your water set to the exact right temp so you don't change the temp too much and shock your fish. Basically if oyu have your tank at 79 and you accidentally put 83 degree water in there that would raise your temp by 2 degrees within minutes and could put your fish into shock. I would stick with the 30 pct water changes and be patient.

will do! thanks

JamesS wrote:


mylutino Im pretty sure tyour required GPH is way off. By your numbers a EHEIM Pro III 2080 would not be enough for a 100 Gal tank.[/quote]

nope a minimum for a good healthy filtration should be 5 times the volume for a canister and 10 times the volume for a HOB. Cichlids are dirty and require heavy filtering. I tried to get by with the bare minimum before had had constand bacterial bloom and I was doing water changes and vaccums religiously. Once I stepped up my flow rate, I was all good.


are you saying my numbers are too high??

so even with the 30 pct. water changes, i have yet to see my ammonia levels go down. when should i be seeing a change?

i went through this before. I started with a large water change 75% and then did daily 25-30% like james suggested. Clean water that can help bring down ammonia is much more beneficial than keeping it in there.

if you keep up on it, it should be clear within a few days. Its hard work but you will be fine!

so you think i should invest in another HOB filter, just like the one i have now?